京东疯狂数列

#include <iostream>
#include <cmath>
using namespace std;

int main() {
	unsigned long long n;
	cin >> n;
        //设第n个数为x，则x*(x+1)/2 = n,求解x, 得到 res = (-1 + sqrt(1 + 8 * n)) / 2;
	int res = ceil((-1 + sqrt(1 + 8 * n)) / 2);
	cout << res << endl;
	return 0;
}