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