#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using Graph = vector<vector<int>>;
#define rep(i,m,n) for(int (i)=(m);(i)<(n);++(i))
#define rREP(i,m,n) for(int (i)=(n)-1;(i)>=(m);--(i))
#define all(x) (x).begin(),(x).end()
#define out(y,x,h,w) (y)<0||(x)<0||(y)>=(h)||(x)>=(w)
constexpr int INF = 1000000001;
constexpr ll mod = 1000000007;
constexpr double PI = 3.1415926535897932;
template<class T>inline bool chmin(T& a, T b) {
	if (a > b) {
		a = b;
		return true;
	}
	return false;
}
template<class T>inline bool chmax(T& a, T b) {
	if (a < b) {
		a = b;
		return true;
	}
	return false;
}
inline void init() {
	cin.tie(nullptr); cout.tie(nullptr);
	ios::sync_with_stdio(false);
	cout << fixed << setprecision(15);
}

int main() {
	init();

	int N; cin >> N;
	int ans = N - (N / 2 + 1) + 1;
	cout << ans << "\n";

	return 0;
}