#include <iostream>
using namespace std;

int main(){
    int N;
    cin >> N;

    cout<<N-1;
}
// #define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
// #include <atcoder/all> // g++ main.cpp -std=c++17 -I .
using namespace std;
// using namespace atcoder;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define all(v) (v).begin(), (v).end()
template<class T,class U> inline bool chmin(T&x,U y){if(x>y){x=y;return true;}return false;}
template<class T,class U> inline bool chmax(T&x,U y){if(x<y){x=y;return true;}return false;}
using ll=long long;

const int inf = INT_MAX / 2; const ll INF = 1LL << 60;
const ll MOD = 1000000007;
// const int MOD = 998244353;

// cout << fixed << setprecision(15) << ans << endl;
// using mint = modint1000000007;

////////////////////////////////////////////////////////////////////////////////////////////


int main() {
  ll n;cin>>n;
  ll k = 0;
  while(k*(k+1)<=2*(n+1)) k++;
  cout << n - (k-2) << endl;
}