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

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

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

    int x;

    x = sqrt(n) + 1;
    for(int i = 2; i<=x; ++i){
        if(p[i]== false){
            for(int j = i*i; j<=n; j+=i){
                p[j] = true;
            }
        }
    }

    for(int i =2; i <=n; ++i) if(p[i]==0) ++k;
    cout<<k;



    return 0;
}