#include <bits/stdc++.h>
#define MAXN 2000005

using namespace std;

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

bitset<MAXN> ciur;
void generare() {
    ciur[0] = ciur[1] = 1;
    for (int i = 4; i < MAXN; i += 2)
        ciur[i] = 1;
    for (int i = 3; i * i < MAXN; i += 2)
        if (!ciur[i])
            for (int j = i * i; j < MAXN; j += 2 * i)
                ciur[j] = 1;
}

int main() {
    generare();
    int n, contor = 0;
    fin >> n;
    for (int i = 2; i <= n; i++)
        if (!ciur[i])
            contor++;
    fout << contor;
    return 0;
}