#include<fstream>
#include<algorithm>
#include<cstring>
#include<vector>
#include<string>
#include<queue>
#define abs(x) ((x>0)?(x):(-(x)))
#define max(a,b) ((a)>(b)?(a):(b))
#define min(a,b) ((a)<(b)?(a):(b))
#define ll long long
using namespace std;
ifstream in("fractii.in");
ofstream out("fractii.out");
const int Nmax = 1000000;
char ciur[Nmax+5];
ll N,S;
int main(){
    in>>N;
    S=N*(N-1)+1;
    S-=(N/2)*(N/2)-(N/2);
    for(int i=3;i<=N;i++){
        if(i%2!=0 && !ciur[i]){
            int j;
            for(j=1;i*j<=N;j++) ciur[i*j]=1;
            j--;
            S-=j*j-j;
        }
    }
    out<<S<<'\n';
    return 0;
}