func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     long long n, k, b, e;     cin >> n >> k;     if (n == 1) {       cout <<  0  << endl;       return 0;     }     long long p = ((k - 1) * k) / 2 - 1;     if (n >= 2 && n <= (p + 2)) {       b = 2;       e = k - 2;       if (n == p + 2)         cout << k - 1 << endl;       else if (n >= 2 && n <= k)         cout <<  1  << endl;       else {         while (b <= e) {           long long mid = (e + b) / 2;           long long g = k - mid + 1;           long long begin = (k * (k + 1)) / 2 - (g * (g + 1)) / 2;           long long f = mid - 2;           begin = begin - f + 1;           g--;           long long end = (k * (k + 1)) / 2 - (g * (g + 1)) / 2;           long long f2 = mid - 1;           end = end - f2;           if (n >= begin && n <= end) {             cout << mid << endl;             break;           } else if (n > end)             b = mid + 1;           else             e = mid - 1;         }       }     } else       cout <<  -1  << endl;     return 0;   }   