【USACO 3.2】Factorials（阶层非零尾数）

/*
TASK:fact4
LANG:C++
*/
#include<cstdio>
#include<algorithm>
#include<cstring>
#define INF 0x3f3f3f3f
using namespace std;
int main(){
    freopen("fact4.in","r",stdin);
    freopen("fact4.out","w",stdout);
    int n,ans=1;
    scanf("%d",&n);
    for(int i=1;i<=n;i++){
        ans*=i;
        while(ans%10==0)ans/=10;
        ans%=1000;
    }
    printf("%d\n",ans%10);
    return 0;
}