#include<bits/stdc++.h>
using namespace std;
int d,dc=1,j=0;
int main(){
    cin>>d;
    for(int i=2;i<=d;i++){
        j++;
        if(j==dc){
            dc++;
            j=0;
        }
    }
    cout<<dc;
    return 0;
}
/**************************************************************
	Problem: 1248
	User: lijinkai
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/