rt,这道题范围只有 $1000000$，不理解我 n sqrt(n)的算法为什么会T

题目

TLE Code

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>

using namespace std;

int l, r;

inline bool ck(int x)
{
	for (int i = 2; i * i <= x; i ++ )
	  if (x % i == 0)
	    return 0;
	
	return 1;
}

int main()
{
	int res = 0;
	cin >> l >> r;
	for (int i = l; i <= r; i ++ )
	 if (ck(i))
	   res ++ ;
	
	cout << res << endl;
	return 0;
}