C++ :

#include <bits/stdc++.h>
using namespace std;
const int N = 210;
int a[N], b[N], c[N], n;
void convert(int a[], string s)
{
	int len = s.size();
	for (int i = 0; i < len; i++)
		if (s[i] >= '0' && s[i] <= '9') 
			a[len-i-1] = s[i] - '0';
		else
			a[len-i-1] = s[i] - 'a' + 10;
}

int main()
{
	cin >> n;
	string s1, s2;
	cin >> s1 >> s2;
	int len1 = s1.size();
	int len2 = s2.size();
	convert(a, s1);
	convert(b, s2);
	int len = max(len1, len2);
	int t = 0;
	for (int i = 0; i < len; i++)	
	{
		t += a[i] + b[i];
		c[i] = t % n;
		t /= n;
	}
	if (t > 0) c[len++] = t;
	for (int i = len - 1; i >= 0; i--)
		if (c[i] >= 10) cout << char(c[i] + 'a' - 10);
		else cout << c[i];
	return 0;
}

Pascal :

program gjdjf;
  var
    a,b,c:array[1..210]of integer;
    lena,lenb,lenc,i,s:longint;

  procedure datain;
    var
      i:longint;
      n1,n2:string;
    begin
      readln(s);
      readln(n1);
      lena:=length(n1);
      readln(n2);
      lenb:=length(n2);
      for i:=1 to lena do
        begin
          case n1[i] of
            '0'..'9':a[lena-i+1]:=ord(n1[i])-48;
            'a'..'z':a[lena-i+1]:=ord(n1[i])-87;
          end;
        end;
      for i:=1 to lenb do
        begin
          case n2[i] of
            '0'..'9':b[lenb-i+1]:=ord(n2[i])-48;
            'a'..'z':b[lenb-i+1]:=ord(n2[i])-87;
          end;
        end;
    end;

  procedure work;
    var
      x,i:longint;
    begin
      i:=1; x:=0;
      while (i<=lena)or(i<=lenb) do
        begin
          c[i]:=a[i]+b[i]+x;
          x:=c[i] div s;
          c[i]:=c[i] mod s;
          inc(i);
        end;
      if x>0 then
        begin
          lenc:=i;
          c[i]:=x;
        end
      else lenc:=i-1;
    end;

  procedure dataout;
    var
      i:longint;
    begin
      for i:=lenc downto 1 do
        begin
          case c[i] of
            0..9:write(c[i]);
            10..35:write(chr(c[i]+87));
          end;
        end;
    end;

  begin
    datain;
    work;
    dataout;
  end.