#include <bits/stdc++.h>

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

int main()
{
    const int LIMIT = 2e6;
    bool prim[LIMIT + 5] = {0};
    int total = 0;

    int x;
    fin >>x;

    for(int i = 2; i < x; ++i)
    {
        if(!prim[i])
        {
            ++total;
            for(int j = i + i; j < x; j += i)
                prim[j] = 1;
        }
    }
    fout << total;
}