#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define rep(i,n) for(int i=0;i<n;i++)
#define riano_ std::ios::sync_with_stdio(false);std::cin.tie(nullptr)

int main() {
    riano_;
    ll N; cin >> N;
    
    //binary search
    ll l,r;
    l = 1; r = min(3*(ll)ceil(sqrt(N)),N);
    
    while(l<r){
        ll c = (l+r)/2;

        //unseen hight
        ll t = N-c; bool ok = false;
        rep(i,c-1){
            ll p;
            if(i==0) p = 2*N-1;
            else p = 2*N-2*i;
            ll len = p-2*t-1;
            t -= len;
            if(t<=0){
                ok = true; break;
            }
        }
        
        if(!ok){
            l = c+1;
        }
        else r = c;
    }
    cout << N-l << endl;
}