#include <bits/stdc++.h>

using namespace std;

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

int n;
int v[2002002];

int main()
{
    fin >> n;
    for(int i = 4; i <= n; i += 2)
    {
        v[i] = 1;
    }
    /// daca v[i] == 0 => i e prim
    int ans = 1;
    for(int i = 3; i <= n; i ++)
    {
        if(!v[i])
        {
            ans++;
            for(int j = i * i; j <= n; j += 2 * i)
            {
                v[j] = 1;
            }
        }
    }
    fout << ans << '\n';
    return 0;
}