#include <bits/stdc++.h>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

bool v[2000001];

int main()
{
    int n, nr;
    f >> n;

        nr = 1;

    for(int i = 3; i <= n; i += 2)
        if(v[i] == 0)
        {
            nr++;
            for(int j = 2 * i; j <= n; j += i)
                v[j] = 1;
        }

        g << nr;

    return 0;
}