VKURI Solution

#include<bits/stdc++.h>
#define ll long long
#define ld long double
#define pb push_back
#define x first
#define y second
#define fastread ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define PI (atan(1)*4)
#define mp make_pair
using namespace std;

int main()
{
    fastread;
    ll n;
    cin >> n;
    cout << (long long)((sqrt(1 + 8 * n) - 1) / 2);
    return 0;
}