#include <fstream.h>
ifstream fin("ciur.in");
ofstream fout("ciur.out");
char v[2000001];
long i,k,n,a;
int main() {
fin>>n;
for (i=2;i<=n;++i)
	v[i]='0';
for (i=2;i<=n;++i)
	if (v[i]=='0')
		{
		for (k=i;i*k<=n;++k)
			if (!v[i*k])
				v[i*k]='1';
		a++;
		}
fout<<a;
return 0;
}