#include <bits/stdc++.h>

using namespace std;

bitset<2000001> a;

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

    int i, j, n;
    fin >> n;
    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])
            for (j = i * i; j <= n; j += 2 * i) a[j] = 1;
    int cnt = 1;
    if (n == 2) fout << cnt;
    else
    {
        for (i = 3; i <= n; i += 2)
            if (!a[i]) cnt++;
    }
    fout << cnt;

    return 0;
}