func_code_string: #include <bits/stdc++.h>   using namespace std;   long long derangements(long long n) {     if (n == 0) return 1;     if (n == 1) return 0;     if (n == 2) return 1;     return (n - 1) * (derangements(n - 1) + derangements(n - 2));   }   long long nCr(long long n, long long r) {     long long res = 1;     if (r == 0) return res;     for (long long i = 0; i < r; i++) res *= (n - i);     for (long long i = 2; i <= r; i++) res /= i;     return res;   }   int32_t main() {     ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);     long long n, k, ans = 0;     cin >> n >> k;     for (long long i = 0; i <= k; i++) ans += (nCr(n, i) * derangements(i));     cout << ans;     return 0;   }   