#include <bits/stdc++.h>

using namespace std;

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

int i, j, n, nr;
bool w[2000005];

int main()
{
    f >> n;
    for(i = 2; i <= n; ++ i)
    {
        if(!w[i])
        {
            nr ++;
            for(j = i + i; j <= n; j += i)
                w[j] = 1;
        }
    }
    g << nr;
    return 0;
}