#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
int main(){
    ll n;
    cin >> n;
    ll l = 0;
    ll r = pow(10,9);
    while(1){
        if(r - l <= 1)break;
        ll mid = (l + r) /2;
        if(mid*mid + mid >= n*2)r = mid;
        else l = mid;
        
    }
    cout << r << endl;
}