#include <iostream>
#include <fstream>
#include <cstring>
#include <iomanip>
#include <algorithm>
using namespace std;

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

const int MAX = 2000000;
int numar;
bool vc[MAX];

void marked_notprim(bool vc[], int numar)
{
    for(int i = 2; i*i <= numar; i++)
    {
        if(vc[i] == 0)
        for(int j = i*i; j <= numar; j=j+i)
            vc[j] = 1;
    }
}

int main()
{
    fin >> numar;
    marked_notprim(vc, numar);
    int sum = 0;
    for(int i = 2; i <= numar; i++)
        if(vc[i] == 0) sum++;
    fout << sum;
    return 0;
}