#include <iostream>
#include <fstream>

using namespace std;

int prime[2000000];
int main()
{
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");

    int n, i, j, nr = 1;
    fin >> n;

    for (i = 3; i <= n; i+=2){
        if (prime[i] == 0){
            nr++;
            for (j = i*i; j <= n; j+= i)
                prime[j] = 1;
        }
    }
    fout << nr;
    return 0;
}