#include<iostream>
#include<fstream>

using namespace std;

ifstream fin("fractii.in");
ofstream fout("fractii.out");
int main(){
	bool prim[100000];
	int n,p,i;
	fin>>n;
	for(i=1;i<=n;++i)	prim[i]=1;
	for(p=2;p*p<=n;++p){
		if(prim[p]){
			for(i=p*p;i<=n;i+=p){
				prim[i]=false;
			}
		}
	}
	int suma=0;
	for(i=2;i<=n;++i)
		if(prim[i])
			suma+=i;
	fout<<2*suma+1;
}