#include <bitset>
#include <cstdio>

const int NMAX = 2 * 1e6;
std::bitset<NMAX> ciur;

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    int n;
    scanf("%d", &n);
    ciur[0] = true;
    for (int i = 2; i * i <= n; ++i)
        if (!ciur[i - 1])
            for (int j = i; i * j <= n; ++j)
                ciur[i * j - 1] = true;
    int cnt = 0;
    for (int i = 2; i <= n; ++i)
        if (!ciur[i - 1])
            ++cnt;
    printf("%d\n", cnt);
    fclose(stdin);
    fclose(stdout);
}