#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000000


int main(){
	
	int N;
	cin>>N;
	
	long long ng = 0LL,ok = Inf;
	
	while(ok-ng>1LL){
		long long mid = (ok+ng)/2;
		
		long long t = mid;
		t *= mid+1;
		t /= 2;
		if(t>=N)ok = mid;
		else ng = mid;
		
	}
	cout<<ok<<endl;
	
    return 0;
}