#54752: 二分法讚讚 (C++)
xutingyao0505@gmail.com
(TingYao Xu)
#include <iostream>
using namespace std;
long long calculate_days (long long S, long long X) {
// 等差求和：(首項 + 末項) * 項數 / 2
// 項數是 (X - S + 1)
return (S + X) * (X - S + 1) / 2;
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
long long S, D;
while (cin >> S >> D) {
long long low = S;
long long high = 2000000000; // 2*10^9 確保涵蓋 D=10^15 的情況
long long ans = S;
while (low <= high) {
long long mid = low + (high - low) / 2;
if (calculate_days(S, mid) >= D) {
ans = mid;
high = mid-1;
} else {
low = mid + 1;
}
}
cout << ans << "\n";
}
return 0;
}