#include <iostream> #include <memory.h> #include <map> #include <string> #include <functional> #include <vector> using namespace std; typedef long long ll; ll n, k; ll fa(ll a) { if (a == 0) return 1; ll res = 1; for (int i = 1; i <= a; i++) res *= i; return res; } ll po(ll a) { if (k == 0) return 1; ll res = 1; for (int i = 0; i < k; i++) res = res * a; return res; } int main() { ios::sync_with_stdio(false); cin >> n >> k; ll res = 0; for (ll i = 0; i <= n; i++) { res = res + (po(fa(i))); } while (1) { if (res == 0) return 0; else if (res % 10 != 0) { cout << res % 10 << endl; return 0; } res = res / 10; } return 0; }