#include <iostream>

int main() {
  unsigned int N;
  std::cin >> N;

  int cnt = 0;
  for (int i = 0; i < N; i++) {
    for (int j = 0; j < N; ++j) {
      if (i+j == N) cnt++;
    }
  }
  std::cout << cnt;
  return 0;
}
#include<bits/stdc++.h>
using namespace std;

int main(){
	int n;
	cin>>n;
	cout<<n-1<<endl;
	return 0;
}