暴力代码求调

#include <bits/stdc++.h>
using namespace std;
int main()
{
    unsigned long long n;
    unsigned long long ans=1;
    cin>>n;
    for(unsigned long long i=1;i<=n;++i)
    {
        while(ans%10==0)
        {
            ans/=10;
        }
        ans=(ans%10)*i;
    }
    while(ans%10==0)
    {
        ans/=10;
    }
    cout<<ans%10;
}