#include<stdio.h>
int n,i,k,j;
char v[2000005];
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    for(i=2;i<=n;i++)
    {

        v[i]=0;

    }
    k=0;
    for(i=2;i<=n;i++)
    {

        if(v[i]==0)
        {
            k++;
            for(j=i+i;j<=n;j=j+i)
            {

                v[j]=1;
            }
        }
    }
    printf("%d",k);
    fclose(stdout);
    return 0;
}