C :

#include<stdio.h>
int main()
{
	int n;
	scanf("%d", &n);
	int a, b, c, d;
	d = n / 1000;
	c = n / 100 % 10;
	b= n % 100 / 10;
	a = n % 10;
	printf("%d%d%d%d", a,b,c,d);
	return 0;
}

C++ :

#include <cstdio>
//#include <cstdlib>
int main(){
  int n;
  scanf("%d", &n);
  printf("%d%d%d%d\n", n%10, n/10%10, n/100%10,n/1000);
//system ("pause");
  return 0;
}

Pascal :

var ch:array[0..5] of char;
    i:longint;
 begin
   for i:=1 to 4 do read(ch[i]);
   for i:=4 downto 1 do write(ch[i]);
  end.