#include <stdio.h>
int c[2000001],j,n,i,nr;
int main(void)
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    nr=1;
    for (i=3;i<=n;i+=2)
    {
        if (c[i]==0)
        {
            nr++;
            for (j=i*i;j<=n;j+=i)
                c[j]=1;
        }
    }
    printf("%d",nr);
    return 0;
}