#include <fstream>
#include <iostream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool v[2000001];
int main()
{
    int n,nr=0;
    in>>n;
    v[1]=1;
    for (int i=2;i<=n;i++){
        if (v[i]==0){
            for (int j=2*i;j<=n;j+=i){
                v[j]=1;
            }
        }
    }
    for (int i=1;i<=n;i++){
        if (v[i]==0){
            nr++;
        }
    }
    out<<nr;
    return 0;
}