#include<stdio.h>
#define input "ciur.in"
#define output "ciur.out"
#define Nmax 2000005
char x[Nmax];
int main()
     {
     freopen(input,"r",stdin);
     freopen(output,"w",stdout);
     int cnt=1000,n,nr=0,rsp[1025],j;
     scanf("%d",&n);
     for(int i=2;i<=n;++i)
          {
          if(x[i]!='0')
                {
                nr++;
                for(j=i*i;(j<=n)&&(i<3000);j+=i) x[j]='0';
                }
          }
     printf("%d\n",nr);
     return 0;
     }