#include <iostream>
#include <fstream>
#include <math.h>
using namespace std;

ifstream fi("ciur.in");
ofstream fo("ciur.out");



int main()
{   int N;
    fi>>N;
    int C[N+1],I, J,S=0,A=sqrt(N);

    fi>>N;

    for(I=1; I<=N; I++) C[I] =1;

    for (I=2; I<=A; I++)

        if(C[I] == 1)

            for(J=2; J*I <= N; J ++)  C[I*J] = 0;


    for(I=2; I<=N; I++)

        if(C[I] ==1) S++;
        fo<<S;
    return 0;
}