C++ :

#include<cstdio>
#include<queue>
#include<cstring>
using namespace std;

queue<int> q;
int rotb1[1001][1001],rotr1[1001][1001];
int rotb2[1001][1001],rotr2[1001][1001];
long long mi1[1002],mi2[1002];
bool d1[1001],d2[1001];

int main()
{
	//freopen("party.in","r",stdin);
	//freopen("party.out","w",stdout);
	int n,m,k,a,b,r;
	long long maxx=0;
	scanf("%d%d%d",&n,&m,&k);
	for (int i=1;i<=m;i++)
	{
		scanf("%d%d%d",&b,&a,&r);
		rotb1[a][++rotb1[a][0]]=b;
		rotr1[a][++rotr1[a][0]]=r;
		rotb2[b][++rotb2[b][0]]=a;
		rotr2[b][++rotr2[b][0]]=r;
	}
	
	memset(mi1,127,sizeof(mi1));
	memset(mi2,127,sizeof(mi2));
	mi1[k]=mi2[k]=0;
	
	q.push(k);
	while (!q.empty())
	{
		int num=q.front();
		q.pop();
		d1[num]=false;
		for (int i=1;i<=rotb1[num][0];i++)
		{
			b=rotb1[num][i];
			r=rotr1[num][i];
			if (mi1[b]>mi1[num]+r)
			{
				mi1[b]=mi1[num]+r;
				if(!d1[b])
				{
					q.push(b);
					d1[b]=true;
				}
			}
		}
	}
	
	q.push(k);
	while (!q.empty())
	{
		int num=q.front();
		q.pop();
		d2[num]=false;
		for (int i=1;i<=rotb2[num][0];i++)
		{
			b=rotb2[num][i];
			r=rotr2[num][i];
			if (mi2[b]>mi2[num]+r)
			{
				mi2[b]=mi2[num]+r;
				if(!d2[b])
				{
					q.push(b);
					d2[b]=true;
				}
			}
		}
	}
	
	
	for (int i=1;i<=n;i++)
		if(maxx<mi1[i]+mi2[i]&&mi1[i]!=mi1[1001]&&mi2[i]!=mi2[1001])
			maxx=mi1[i]+mi2[i];
	
	printf("%lld",maxx);
	return 0;
	
}

Pascal :

program party;
type
  edge=record
    x,w,next:longint;
  end;
var
  e,e2:array[0..200000]of edge;
  k,k2:array[0..2000]of longint;
  v:array[0..2000]of boolean;
  d,d2:array[0..2000]of longint;
  f:array[0..1000000]of longint;
  i,j,m,n,kk,x,y,z,ans:longint;
  tot,tot2:longint;
procedure add(x,y,z:longint);
  begin
    inc(tot);
    e[tot].x:=y;
    e[tot].w:=z;
    e[tot].next:=k[x];
    k[x]:=tot;
  end;
procedure add2(x,y,z:longint);
  begin
    inc(tot2);
    e2[tot2].x:=y;
    e2[tot2].w:=z;
    e2[tot2].next:=k2[x];
    k2[x]:=tot2;
  end;
procedure SPFA1;
  var
    head,tail,t,x:longint;
  begin
    head:=0;
    tail:=1;
    f[tail]:=kk;
    fillchar(v,sizeof(v),0);
    fillchar(d,sizeof(d),63);
    d[kk]:=0;
    v[kk]:=true;
    while (head<tail) do
      begin
        inc(head);
        x:=f[head];
        v[x]:=false;
        t:=k[x];
        while (t<>0) do
          begin
            if (d[e[t].x]>d[x]+e[t].w) then
              begin
                d[e[t].x]:=d[x]+e[t].w;
                if (not v[e[t].x]) then
                  begin
                    v[e[t].x]:=true;
                    inc(tail);
                    f[tail]:=e[t].x;
                  end;
              end;
            t:=e[t].next;
          end;
      end;
  end;
procedure SPFA2;
  var
    head,tail,t,x:longint;
  begin
    head:=0;
    tail:=1;
    f[tail]:=kk;
    fillchar(v,sizeof(v),0);
    fillchar(d2,sizeof(d2),63);
    d2[kk]:=0;
    v[kk]:=true;
    while (head<tail) do
      begin
        inc(head);
        x:=f[head];
        v[x]:=false;
        t:=k2[x];
        while (t<>0) do
          begin
            if (d2[e2[t].x]>d2[x]+e2[t].w) then
              begin
                d2[e2[t].x]:=d2[x]+e2[t].w;
                if (not v[e2[t].x]) then
                  begin
                    v[e2[t].x]:=true;
                    inc(tail);
                    f[tail]:=e2[t].x;
                  end;
              end;
            t:=e2[t].next;
          end;
      end;
  end;
begin
  
  readln(n,m,kk);
  for i:=1 to m do
    begin
      readln(x,y,z);
      add(x,y,z);
      add2(y,x,z);
    end;
  SPFA1;
  SPFA2;
  ans:=0;
  for i:=1 to n do
    if (i<>kk)and(d[i]<1000000)and(d2[i]<1000000) then
    begin
      if (d[i]+d2[i]>ans) then ans:=d[i]+d2[i];
    end;
  writeln(ans);
  
end.