#include <stdio.h>



int N, cnt;

char prim[2000005];



int main(void)

{

    int i, j;



    freopen("ciur.in", "r", stdin);

    freopen("ciur.out", "w", stdout);



    scanf("%d", &N);

    for (i = 2; i <= N; ++i)

        prim[i] = 1;

    for (i = 2; i <= N; ++i)

        if (prim[i])

        {

            ++cnt;

            for (j = i+i; j <= N; j += i)

                prim[j] = 0;

        }



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



    return 0;

}