#include <bits/stdc++.h>
using namespace std;

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

bitset<2000000> a;
int n;

int main()
{
    int i , j , cnt;
    n = 2000000;
    a[0] = a[1] = 1;
    for (i = 4 ; i <= n ; i += 2)
        a[i] = 1;
    for (i = 3 ; i * i <= n ; i += 2)
        if (a[i] == 0)
            for (j = i * i ; j <= n ; j += 2 * i)
                a[j] = 1;
    fin >> n;
    cnt = 0;
    for (i = 2 ; i <= n ; i++)
        if (a[i] == 0) cnt++;
    fout << cnt << "\n";
    return 0;
}