#include <stdio.h>
#define FIN "ciur.in"
#define FOUT "ciur.out"
#define nmax 2000001
char v[nmax+1];
long n,i,j,ct;

int main()
{
 freopen(FIN,"rt",stdin);
 freopen(FOUT,"wt",stdout);
 scanf("%d",&n);
 for(i=1;i<=n;++i)
 v[i]=1;

 for(i=2;i<=n;++i)
     if(v[i]==1)
	{++ct;
	 for(j=i+i;j<=n;j+=i)
	    v[j]=0;
	}

 printf("%d",ct);

 return 0;
}