#include <bits/stdc++.h>

using namespace std;

bitset<2000003> a;

int main()
{
    int n, i, j, cnt;
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin >> n;
    for (i = 2; i * i <= n; ++i)
        if (a[i] == 0)
            for (j = i * i; j <= n; j = j + i)
                a[j] = 1;
    cnt = 0;
    for (i = 2; i <= n; ++i)
        if (a[i] == 0)
            cnt++;
    fout << cnt << "\n";
    fin.close();
    fout.close();
    return 0;
}