末位数的，100% #include <bits/stdc++.h> using namespace std; int main() { int n; cin >> n; long long sum = 1; for (int i = 1; i <= n; ++i) { sum *= i; while (0 == (sum % 10)) { sum = sum / 10; } if (sum > 100000000) { sum = sum % 100000000; } } if (0 == n) { sum = 0; } cout << sum % 10 << endl; }