#include<stdio.h>

long n,e;
char p[2000001];

int main()
{ freopen("ciur.in","r",stdio);
    scanf("%l",&n);
      for(long i=2;i<=n;i++)
        p[i]=1;
	for(long i=2;i<=n;i++)
		if(p[i])
                  { e++;	
            	  for(long j=i+i;j<=n;j+=i)
		  	p[j]=0;
 		}	
    printf("%d",e);
    return 0;
}