#include <fstream>
#include <cmath>
using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

bool p[2000005];
unsigned int prim[50000];
int k = 0;
int main()
{
    long n;
    cin>>n;

    int x;

    x = sqrt(n) + 1;

    for(int i =2; i<=n; ++i){
        if(p[i]== false){
            prim[k++] = i;
            for(int j = 2*i; j<=n; j+=i){
                p[j] = true;
            }
        }
    }
    cout<<'\n'<<k;



    return 0;
}