#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
using namespace std;

typedef long long ll;

int main() {
    ll N;
    cin >> N;
    ll ok = N, ng = 0;
    while (ng + 1 < ok) {
        ll md = (ok + ng) / 2;
        if (md * (md + 1) / 2 >= N) ok = md;
        else ng = md;
    }
    cout << ok << "\n";
}