#include <stdio.h>

int N, cnt;

int prim(int X)
{
    int i;

    for (i = 2; i * i <= X; ++i)
        if (X % i == 0)
            return 0;
    return 1;
}

int main(void)
{
    int i;
    
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    scanf("%d", &N);
    for (i = 2; i <= N; ++i)
        if (prim(i))
            ++cnt;
    printf("%d\n", cnt);

    return 0;
}