#include<stdio.h>
int main()
{ 
	long int n,i,j,contor=0;
	bool v[2000002];
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);
	scanf("%ld",&n);
	 for(i=2;i<=n;++i)   
      {if(!v[i])   
        {contor++;   
         for(j=2;j*i<=n;++j) v[i*j]=1;   
        } }  

	 printf("%ld", contor); return 0;
}