#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int n, ans;
bool viz[2000005];

int ciur() {
    for (int i = 2; i * i <= n; i++) {
        if (!viz[i])
            for (int j = i * i; j <= n; j += i)
                viz[j] = true;
    }
    for (int i = 2; i <= n; i++)
        if (!viz[i])
            ans++;
    return ans;
}

int main(int argc, const char * argv[]) {
    fin >> n;
    fout << ciur();
}