Contest1120/C.cpp

#include<bits/stdc++.h>

using namespace std;

bool prime(int n) {
    if (n == 2)return true;
    if (n % 2 == 0 || n < 2)return false;
    for (int c = 3; c * c <= n; c += 2)
        if (n % c == 0)return false;
    return true;
}

int solve(int n) {
    int tot = 0;
    int p = n >> 1;
    if (p % 2 == 0)--p;
    for (; p >= 3; p -= 2)
        if (prime(p) && prime(n - p)) {
            ++tot;
        }
    return tot;
}

int main() {
    for (int n; cin >> n;)
        cout << solve(n) << endl;
    return 0;
}