HDU 2138-How many primes?

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#include <iostream>
#include <algorithm>
#include <numeric>
#include <bitset>
#include <vector>
#include <stack>
#include <cstdio>
#include <cstring>
#include <cmath>

using namespace std;

#define fe(i, a, b) for (int i = int(a); i <= int(b); i++)
#define fu(i, a, b) for (int i = int(a); i < int(b); i++)
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<bool> vb;
typedef vector<vb> vvb;
typedef pair<int, int> pii;
#define pb push_back
#define mp make_pair

bool prime(int a)
{
    if (a < 2) return false;
    if (a == 2 || a == 3) return true;
    if (!(a & 0x01)) return false;
    int m = floor(sqrt((double)a) + 0.5);
    //cout << a << ":" << m << endl;
    for (int i = 3; i <= m; i += 2) {
        if (a % i == 0) return false;
    }
    return true;
}

int main()
{
    int n;
    int a, count;
    while (cin >> n) {
        count = 0;
        while (n--) {
            cin >> a;
            if (prime(a)) count++;
        }
        cout << count << endl;
    }

    return 0;
}