#include <bits/stdc++.h>

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int n;
bool ciur[2000005];
int main()
{
    in >> n;
    int ans = 0;
    for (int i = 2; i <= n; i++) {
        if (ciur[i] == 0) {
            ans++;
            for (int j = 2; i * j <= n; j++)
                ciur[i * j] = 1;
        }
    }
    out << ans;
    return 0;
}