#include<fstream.h>
ifstream f("ciur.in");
ofstream g("ciur.out");
int x,i,j,np;
char prim[2000001];
int main()
{f>>x;
 for(i=2;i<=x;i++) prim[i]=1;
	if(!prim[i])
		{
		 np++;
		 for(j=i+i;j<=x;j+=i) prim[j]=1;
		}
 
g<<np;	
g.close();
return 0;	
}
/*#include<stdio.h>
int n,nr,i,j;
bool a[2000001];
int main()
{
 freopen("ciur.in","rt",stdin);
 freopen("ciur.out","wt",stdout);
 scanf("%d",&n);
 for(i=2;i<=n;i++)
	if(!a[i]) 
		{
		 nr++;
		 for(j=i+i;j<=n;j+=i) a[j]=1;
		}
 printf("%d",nr);
 return 0;*/