poj 3978 Primes

#include <iostream>
using namespace std;

const int MAX = 100010;
int prime[MAX];

int main()
{
    int i, j, a, b, ans;
    prime[0] = false, prime[1] = false;
    for (i = 2; i < MAX; i++)
         prime[i] = true;
    for (i = 2; i < MAX; i++){
        if (prime[i]){
            for (j = 2; j * i < MAX; j++){
                prime[i*j] = false;
            }
        }
    }
    
    while (cin >> a >> b){
          if (a == -1 && b == -1)   break;
          ans = 0;
          for (i = a; i <= b; i++){
              if (prime[i])
                  ans++;
          }
          cout << ans << endl;
    }
    
    system("pause");
}