#include<iostream>
#include<algorithm>
#include<vector>
#include<cstdio>
using namespace std;

int main(){
    unsigned long long N;
    cin >> N;
    for(long long  i=0;;i++){
        if(N*2<=(i*(i+1))){
              cout << i;
              return 0;
        }
    }
    return 0;
}