#include <cstdio>

int a, nr;
int prim[20000000];

int main(void)
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    int i, j;
    scanf("%d", &a);
    for (int i = 2; i <= a; i++)
        prim[i] = 1;
    for (int i = 2; i <= a; i++)
        if (prim[i])
        {
            nr++;
            for (int j = i+i; j <= a; j += i)
                prim[j] = 0;
        }

    printf("%d\n", nr);

    return 0;
}