#include <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()

template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }

typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS  = 1e-10;

int main() {
	ll n;
	cin >> n;
	
	ll l = 0, r = 10000000000000ll;
	
	while (r - l > 1) {
		ll m = (l + r) / 2;
		
		bool ok = false;
		
		FOR(a, 1, n + 1) {
			ll b = n - a;
			if (a + b + a * b >= m) ok = true;
		}
		
		if (ok) l = m;
		else r = m;
	}
	
	cout << l << endl;
	
	return 0;
}