#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");
int N, cnt, i, j, c[100], m;

int main()
{
    fin >> N;
    if (N == 1)
        fout << "0";
    else {
            cnt = 1;
        for (i = 3; i <= N; i += 2) {
            if (!c[i]) {
                for (j = 2; j * i <= N; ++j) {
                    c[j * i] = 1;
                }
            ++cnt;
            }
        }
        fout << cnt;
    }
    return 0;
}