#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include <map>

using namespace std;

#define INF 		2000000007
#define MOD			1000003

#define MAX 		105

#define REP(i,n)	for(int i=0;i<(n);++i)
#define REPS(i,s,t)	for(int i=(s);i<(t);++i)

typedef unsigned int 			uint;
typedef unsigned long long int	ull;
typedef long long int ll;

int DP[20005];

char itoc(int n){
	return (char)'A'+n;
}

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

	ull a=(N-1)/2;
	ull b=N-a;
	ull ans =b+a+a*b; 
	cout << ans << endl;

	return 0;
}