1 #include<iostream> 2 #include<cmath> 3 4 using namespace std; 5 6 int prime(int n) 7 { 8 int i; 9 for (i=2; i<sqrt(n)+1; i++) 10 { 11 if (n%i == 0) return 0; 12 } 13 return 1; 14 } 15 16 int main() 17 { 18 int n, i; 19 int cnt; 20 while(cin >> n, n) 21 { 22 cnt=0; 23 for (i=n/2-1; i>1; i--) 24 { 25 if (prime(i) && prime(n-i)) 26 { 27 cnt++; 28 } 29 } 30 cout << cnt << endl; 31 } 32 return 0; 33 }