#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;
    int cnt = 0;
    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;
}