#include<stdio.h>
#define DIM 2000000
int n,q,k;
char a[DIM];
int main ()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int i,j;
    scanf("%d",&n);
    for(i=2;i<=n;++i)
        if(!a[i])
        {
            ++k;
            for(j=i;j<=n;j+=i)
                a[j]='1';
        }
    printf("%d",k);
    return 0;
}