建议加强数据

#include <bits/stdc++.h>
#define F(i, a, b) for (int i = a; i <= b; i++)
#define endl "\n"
using namespace std;
typedef long long ll;
int main()
{
    int n;
    cin >> n;
    ll ans = 1ll;
    F(i, 2, n)
    {
        ans *= i;
        while (ans % 100000000000 == 0)
        {
            ans /= 100000000000;
        }
        ans %= 100000000000;
    }
    while (ans % 10 == 0)
    {
        ans /= 10;
    }
    ans %= 10;
    cout << ans;
}