#include <algorithm>
#include <iostream>

using namespace std;

typedef long long ll;

ll n;

ll f(ll x) {
    return abs((x * x + x) - (n * n + n) / 2);
}

int main() {
    cin >> n;
    ll left = 0;
    ll right = n + 1;
    for (; left + 1 < right; ) {
        ll middle = (left + right) / 2;
        f(middle - 1) < f(middle) ? right = middle : left = middle;
    }
    cout << left << endl;
    return 0;
}