#include <stdio.h>

int n, nr;
char p[2000005];

int main()
{
    int i, j;

    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    scanf("%d", &n);
    for (i = 2; i <= n; ++i)
        p[i] = 0;
    for (i = 2; i <= n; ++i)
        if (p[i] == 0)
        {
            ++nr;
            for (j = i + i; j <= n; j+= i)
                p[j] = 1;
        }

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

    return 0;
}