#include <iostream>
#include <fstream>

#define MAX 2000000
using namespace std;
int main() {

    fstream f("ciur.in",ios::in);
    fstream g("ciur.out",ios::out);

    int n,contor = 1;
    f >> n;
    int nums[MAX] = {0};

    for(int i=3;i<=n;i=i+2) {

        if( nums[i] == -1)
            continue;

        int ok = 1;
        for(int j=3;j<i;j++)
            if ( i% j == 0)
                ok = 0;

        if(ok == 1) {
            contor ++;
            int k = 2*i;
            while ( k<= n) {
                nums[k] = -1;
                k+= i;
            }
        }


    }

    g<< contor;

}