#include <cstdio>
using namespace std;
int n;
long long ans=1;
int main(){
scanf("%d",&n);
for(register int i=1;i<=n;i++){
ans*=i;
while(ans%10==0)ans/=10;
ans%=100000000;
}
printf("%lld\n",ans%10);
return 0;
}
原文：http://www.cnblogs.com/codetogether/p/7634829.html