#include<stdio.h>
FILE *in=fopen("ciur.in","r");
FILE *out=fopen("ciur.out","w");
int main()
{
 char v[2000001];

 long int i,n,nr=1,j;
 fscanf(in,"%ld",&n);
 for(i=0;i<=n;i++) v[i]=0;
 for(i=3;i<=n;i=i+2)
 {
	if(v[i]==0)
	{
	 nr++;
	 for(j=i+i+i;j<=n;j=j+2*i)
			v[j]=1;
	}
 }
 fprintf(out,"%ld",nr);
 return 0;
}