#include<fstream>
using namespace std;
char c[10000];
int main()
{int n,i,j,s=0;
ifstream f("a");
ofstream g("b");
f>>n;
for(i=2;i<=n;++i)
	if(!c[i])
		{s++;
		for(j=2*i;j<=n;j+=i)
			c[j]=1;}
g<<s;
}