#include<fstream.h>
int main()
{
int n,i,j,k=0;
char c[1000]={0};
ifstream in("ciur.in");
ofstream out("ciur.out");
in>>n;
for (i=1;i<=n;i++)
    c[i]=i;
for (i=3;i<=n;i++)
   if (i%2==0) c[i]=0;
for (i=1;i*i<=n;i++)
    if (c[i]==0)
	for (j=i*i;i<=n;j+=i)
	   c[j]=1;
for (i=2;i<=n;i++)
   if (c[i]==0) k++;
out<<k;
in.close();
out.close();
return 0;
}