#include <iostream>
#include <fstream>
using namespace std;

char v[2000001];
int counter;

int main() {
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int n;
    fin >> n;
    v[0] = v[1] = -1;
    for (int i = 4; i <= n; i += 2) {
        v[i] = -1;
    }
    for (int i = 3; i * i <= n; i += 2) {
        if(v[i] != -1) {
            for (int j = i * i; j <= n; j = j + 2 * i) {
                v[j] = -1;
            }
        }
    }
    for (int i = 1; i <= n; ++i) {
        if (v[i] != -1)
            ++counter;;
    }
    fout << counter;
    return 0;

}