#include <stdio.h>

const int max=2000000;
char vec[max];

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);

int n,i,j,nr=0;
scanf("%d",&n);
for(i=2;i<=n;i++)
vec[i]=1;
for(i=2;i<=n;i++)

    if(vec[i]!=0)
    {
       nr++;
       for(j=i+i;j<=n;j+=i)
       vec[j]=0;
       }
       
printf("%d",nr);
return 0;
}