Quadratic equation in Dart

import 'dart:io';
import 'dart:math' show sqrt;
int readInt() {
 String input = stdin.readLineSync();
 return int.parse(input);
}
main() {
 int A, B, C;
 try {
 A = readInt();
 B = readInt();
 C = readInt();
 }
 on FormatException {
 print("Coefficient is not a number.");
 return;
 }
 if (A == 0) {
 print("Not a quadratic equation.");
 return;
 }
 int D = B * B - 4 * A * C;
 double p1 = - B / 2.0 / A;
 double p2 = sqrt(D.abs()) / 2.0 / A;
 if (D == 0) {
 print("x = $p1");
 } else {
 if (D > 0) {
 print("x1 = ${p1 + p2}");
 print("x2 = ${p1 - p2}");
 } else {
 print("x1 = ($p1, $p2)");
 print("x2 = ($p1, ${-p2})");
 }
 }
}