C :

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int gcd(int x,int y)
{
    return y==0?x:gcd(y,x%y);
}
int main()
{
	int a,b;
    scanf("%d%d",&a,&b);
    printf("%d",gcd(a,b));
	return 0;
}

C++ :

#include<cstdio>
using namespace std;

int gcd(int xx,int yy)
{
 if(xx==0) return yy;
 else return gcd(yy%xx,xx);
}
int main()
{
    int a,b,t;
    scanf("%d%d",&a,&b);
    
    printf("%d\n",gcd(a,b));
    
    return 0;
}

Pascal :

Program ygjngerb;
  var
    a,b:integer;
  function f(a,b:integer):integer;
  var
    i:integer;
  begin
      f:=0;
      for i:=b downto 1 do
      if (a mod i=0) and (b mod i=0) and (i>f) then f:=i;
      if (f=1) then f:=5;
  end;
  begin
    read(a,b);
    write(f(a,b));
  end.