#include <cstdio>
int n, nr;
char prim[2000005];
int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &n);
    for (int i = 2; i <= n; ++i)
        prim[i] = 1;

    for (int i = 2; i <= n; ++i)
        if (prim[i])
        {
            ++nr;
            for (int j = i*i; j <= n; j += i)
                prim[j] = 0;
        }

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

    return 0;
}