C :

#include<stdio.h>
int xx(int a,int b)
{
    int m,n;
    if(b%2==0)
    {
        m=a*a%1000;
        n=xx(m,b/2);
        return n%1000;
    }
    else if(b==1)
    return a;
    else
    {
        m=a*a%1000;
        n=xx(m,b/2);
        return n*a%1000;
    }
}
int main()
{
    int A,B,i;
    while(scanf("%d %d",&A,&B)!=EOF)
    {
        if(A==0&&B==0)
        break;
        i=xx(A%1000,B);
        printf("%d\n",i);
    }
}

C++ :

#include <stdio.h>
void run(int a,int b)
{
	int i,sum=1;
	a%=1000;
	for(i=1;i<=b;i++)
		sum=sum*a%1000;
	printf("%d\n",sum);
}
int main()
{
	int a,b;
	scanf("%d%d",&a,&b);
	while((a!=0)||(b!=0))
	{
		run(a,b);
		scanf("%d%d",&a,&b);
	}
	return 0;
}