#include<fstream.h>
#define nmax 2000001
char nr[nmax];
long long i,n,j,x[1002],p=0,k=0;
int main(){
ifstream f("ciur.in");
ofstream g("ciur.out");

f>>n;

for(i=2;i<=n;i++)
      if(nr[i]!=1)
	 {k++;
	 for(j=i+i;j<=n;j+=i)
	      nr[j]=1;
	 }
g<<k;
return 0;
}