#include <iostream>
#include <fstream>

using namespace std;

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

int main()
{
    int n, contor = 0;
    char v[2000005];
    fin >> n;
    for(int i = 2; i <= n; ++i) {
        v[i] = 1;
    }
    for(int i = 2; i <= n; ++i) {
        if(v[i]) {
                contor++;
            for(int j = i + i; j <= n; j += i) {
                v[j] = 0;
            }
        }
    }
    fout << contor;
    return 0;
}