C :

#include <stdio.h>
main(){
	int n,t=-1,i=0,a[255];char s[255];
	gets(s);
	while(s[i]!='@'){n=0;
		while(s[i]>='0'&&s[i]<='9'){
			n=n*10+s[i]-'0';i++;	
		}
		if(n!=0){++t;a[t]=n;} 
		if(s[i]=='+'){a[t-1]=a[t-1]+a[t];t--;}
		if(s[i]=='-'){a[t-1]=a[t-1]-a[t];t--;}
		if(s[i]=='*'){a[t-1]=a[t-1]*a[t];t--;}
		if(s[i]=='/'){a[t-1]=a[t-1]/a[t];t--;}
		i++;
	}
	printf("%d ",a[0]);	
} 

C++ :

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cstdlib>
#include<cctype>
#include<stack>
#define num x
using namespace std;


stack<int>num,sym;
int a[255];
char s[300];
int main(){
	/*freopen("strs.in","r",stdin);
	freopen("strs.out","w",stdout);//*/
	char ch;
	ch=getchar();
	while(ch!='@'){
		int k=0;
		while(isalnum(ch)){
			k=k*10+ch-48;
			ch=getchar();
		}
		//cout<<k<<' ';
		if(!(ch!='0'&&k==0))num.push(k);
		while(ch==' ')ch=getchar();
		//cout<<ch;
		
		
		
		if(!isalnum(ch)){
			if(ch=='+'){
				int k1=x.top();	x.pop();
					int k2=x.top(); x.pop();
					x.push(k1+k2);
			}
				else if(ch=='-'){
					int k1=x.top();	x.pop();
					int k2=x.top(); x.pop();
					//cout<<k1<<' '<<k2;
					x.push(k2-k1);
				}	
				else if(ch=='*'){
					int k1=x.top();	x.pop();
					int k2=x.top(); x.pop();
					x.push(k2*k1);
				}	
				else if(ch=='/'){
					int k1=x.top();	x.pop();
					int k2=x.top(); x.pop();
					x.push(k2/k1);
				}	
				ch=getchar();
				while(ch==' ')ch=getchar();
		}
	
	}
	int k=x.top();
	cout<<k;
	//while(1);
	return 0;
}

Pascal :

program track;var t1:array[1..10000] of longint;    top,n,i:integer;    rd:char;    f:boolean;begin   rd:=' ';   top:=0;   f:=false;   while rd<>'@' do      begin         read(rd);         n:=0;         while (rd in ['0'..'9']) do            begin               f:=true;               n:=n*10+ord(rd)-ord('0');               read(rd);            end;         if f then begin         inc(top);         t1[top]:=n;         f:=false;end;         if rd in ['+','-','*','/'] then            begin               case rd of                  '+':t1[top-1]:=t1[top-1]+t1[top];                  '-':t1[top-1]:=t1[top-1]-t1[top];                  '*':t1[top-1]:=t1[top-1]*t1[top];                  '/':t1[top-1]:=t1[top-1] div t1[top];                  end;               dec(top);            end;      end;   write(t1[1]);end.