infoarena informatica de performanta

#include<iostream.h>
#include<fstream.h>
ifstream fin("fractii.in");
ofstream fout("fractii.out");
void fractii(long long n){
	long long i,s=0;
	for(i=2;i<=n/2;i++)
	s=s+((n/i)-1)*(i+1);
	s=s+n-1;
	s=s-(n/2)+1;
	fout<<n*n-s<<endl;
}
int main(){
long long n;
fin>>n;
fractii(n);
return 0;
}