#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;

}