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");
}