#include <fstream>

using namespace std;

bool ciur[2000001];

int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int n;
    fin >> n;
    ciur[0] = 1;
    ciur[1] = 1;
    for (int d = 2; d * d <= 2000000; d++)
    {
        if (!ciur[d])
        {
            for (int i = d * d; i <= 2000000; i += d)
            {
                ciur[i] = 1;
            }
        }
    }
    int ans = 0;
    for (int i = 2; i <= n; i++)
    {
        ans += !ciur[i];
    }
    fout << ans;
    return 0;
}