#include <cstdio>

using namespace std;

bool sieved[2000005];
int main()
{
    int i, n;
    int j, cnt;
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    scanf("%d", &n);
    cnt = 0;
    for (i = 2; i <= n / 2; i++)
    {
        if (!sieved[i])
        {
            for (j = i * 2; j <= n; j += i)
                sieved[j] = 1;
            cnt++;
        }
    }
    cnt += !sieved[j];
    printf("%d\n", cnt);
    return 0;
}