#include <iostream>
using namespace std;
int main(void) {
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	unsigned short n,i,db=0,j;
	cin >> n;
	unsigned short v[n];
	for (i=2;i<=n;i++) 
		v[i]=i;
	i=2;
	while (i<=n) {
		while (v[i]==0) i++;
		db++;
		for (j=i+1;j<=n;j++) {
			if (v[j] % v[i] == 0) v[j]=0;
		}
		v[i]=0;
	}
	cout << (db-1);
}