#include <bits/stdc++.h>
using namespace std;
using ll = long long;
vector<bool>isPrime;
void seive(int n){
	isPrime.resize(n+1,true);
	isPrime[0] = isPrime[1] = false;
	for(int i = 2 ; i < n ;i++ ){
		if(isPrime[i]){
			for(int j = i*i ; j < n ;j+=i){
				isPrime[j]=false;
			}
		}
	}
}
int main() {
	int n;
	cin>>n;
	seive(n);
	int p;
	for(int i = n-1 ; i>=0 ;i--){
		if(isPrime[i]){
			p = i;
			break;
		}
	}
	cout<<"p: "<<p <<endl;
	ll d = 1LL*p*n;
	cout<<"d : " <<d <<endl;
	ll ans = 0;
	if(d%2 == 0)ans = d/2;
	else ans =((n-1)*p+2)/2;
	
	cout<<ans;
}