#include <bits/stdc++.h>

using namespace std;

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

bool p[2000001];

int n ,i ,j ,nr;

int main()
{
    nr = 1;
    f >> n;
    for (i = 3; i <= n; i = i + 2)
    {
        if (p[i] == 0)

        {
            nr++;
            for (j = i + i; j <= n; j = j + i)
               p[j] = 1;
        }
    }
    g << nr;
    return 0;
}