#include <fstream>
#include <bitset>
#define NMAX 2000000

std::bitset<NMAX+1> ciur;
int n, cnt;

int main() {
    ciur[0] = ciur[1] = true;
    for (int i = 2; i * i <= NMAX; ++i) {
        if (!ciur[i])
            for (int j = i * i; j <= NMAX ; j += i) {
                ciur[j] = true;
            }
    }
    std::ifstream in("ciur.in");
    in >> n;
    for (int i = 2; i <= n; ++i) {
        if(!ciur[i])
            ++cnt;
    }
    in.close();
    std::ofstream out("ciur.out");
    out << cnt;
    out.close();
    return 0;
}