#include <fstream>

using namespace std;

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

bool v[2000001];
int n, i, j, prime;

int main()
{
    in >> n;
    if(n >= 2)
        prime++;
    for(i = 3; i <= n; i += 2)
        if(v[i] == 0)
        {
            prime++;
            for(j = i * 2; j <= n; j += i)
                v[j] = 1;
        }
    out << prime;
    return 0;
}