#include <fstream>

using namespace std;

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

const int NMAX = 2000005;
bool divide[NMAX];

int main(int argc, char** argv) {
    int N, count;
    fin >> N;

    for(int i = 2 ; i <= N ; i++) {
        if(!divide[i]) {
            count++;
            for(int j = i * i ; j <= N ; j += i) {
                divide[j] = true;
            }
        }
    }

    fout << count;

    return 0;
}