#include <iostream>
#include<fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool v[1000000000];
int main()
{int n,i,j,nr=0;
    fin>>n;

    for(i=2;i<=n/2;i++)
        if(v[i]==0)
        {//v[i]=7;

        for(j=2;j*i<=n;j++)
        v[j*i]=1;

        }
     for(i=2;i<=n;i++)
        if(v[i]==0)
        nr++;

     fout<<nr;

    return 0;
}