#include <iostream>
#include <fstream>
#include <bitset>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n, sol;
bitset<2000010> prim;

int main() {
    fin >> n;

    for (int i = 2; i * i <= n; i++)
        if (!prim[i])
            for (int j = i * i; j <= n; j += i)
                prim[j] = 1;

    for (int i = 2; i <= n; i++)
        if (!prim[i])
            sol++;

    fout << sol;
    return 0;
}