#include<fstream.h>
#include<iostream.h>
int a,n,i;
char x[2000000];
int main()
{ifstream in("ciur.in");
ofstream out("ciur.out");
in>>n;
x[1]=1;
for(i=2;i<=n;i++)
{
	if(x[i]==0) 
		for(int j=2*i;j<=n;j+=i) x[j]=1;
}
for(i=1;i<=n;i++)
	if(x[i]==0) a++;
out<<a<<endl;
in.close();
out.close();
return 0;
}