[USACO] 3-2-1 Factorials

/*
ID: 551100k1
LANG: C++
TASK: fact4
*/
#include<stdio.h>
int main(){
    freopen("fact4.in","r",stdin);
    freopen("fact4.out","w",stdout);
    int n,i,ans=1;
    scanf("%d",&n);
    for(i=n;i>0;i--){
        ans=ans*i;
        while(ans%10==0) ans/=10;
        ans%=10000;
    }
    while(ans%10==0) ans/=10;
    ans%=10;
    printf("%d\n",ans);
}