#include<iostream>
#include<fstream>
using namespace std;
int main(){

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

    int n,sum=-1;
    fin>>n;
    bool v[n];

    for(int i=0;i<n;++i){

        v[i]=0;
    }

    for(int i=2;i<=n;++i){

        if(v[i]==1)continue;
        for(int j=i*i;j<=n;j=j+i){

            v[j]=1;++sum;
        }
    }

    fout<<sum;
}