#include <iostream>
#include <map>
#include <cmath>
#include <queue>
#include <vector>
#include <string>
#include <algorithm>
#include <functional>
using namespace std;
#pragma warning (disable: 4996)

long long N, minx = (1LL << 30);

int main() {
	cin >> N;
	for (long long i = 1; i <= 100000; i++) {
		long long border = i * (i + 1LL) / 2LL;
		if (border >= N) minx = min(minx, i);
	}
	cout << minx << endl;
	return 0;
}