#include<cstdio>
using namespace std;
const int N = 2000005;
char v[N];
int nr, n;
int ciur(int n)
{
         int i,j;
	for(i = 2 ; i <= n ; ++i)
		if(!v[i])
		{
		nr++;
		for(j=i+i;j<= n;j+=i)
			v[j] = true;
		}
	return nr;
}
int main(){		freopen("ciur.in","r",stdin);		freopen("ciur.out","w",stdout);
		scanf("%d", &n);
		printf("%d\n", ciur(n));
		return 0;
}