Implement the area of a trapezoid in Java

I have to mplement a static-public method named "trapezoidArea" in the class "Functionality.java", which should calculate the area of a trapezoid. The method gets as input parameters the two parallel sides a and c; and the height h as integer values. The method returns a double value.trapezoidArea(a : int, c : int, h : int) : double. I also have to pay attention to the early data type conversion (casting). If at least one of the input values is <= 0, -1.0 should be returned.

So this is the code: But its not working

public class Functionality {

public static double trapezoidArea(int a, int c, int h) {

    double input  = 0;
    if (input <= 0) {
        input = 0.5 * (a + c) * h;
        return input;
    } else if (a <= 0 || c <= 0 || h <= 0) {
        return -1.0;
    }
    return input;
}