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

ifstream fin("ciur.in");
ofstream fout("ciur.out");

bool v[2000001];

int main()
{int n,nr=0;
    fin>>n;

    int in=2;
    for(int i=2;i<=n;i++){
        if(v[i]==0){
            nr++;
            int x=i;
            while(x*in<n){
                v[x*in]=1;
                x++;
            }
        in++;
        }else continue;
    }

    fout<<nr;

    return 0;
}