import Foundation

// Complete the kangaroo function below.
func kangaroo(x1: Int, v1: Int, x2: Int, v2: Int) -> String {
    var currentLocation1 = x1
    var currentLocation2 = x2
    var (differenceInLocations, greaterOne): (Int, Int) = {
        if x1 < x2 {
            return (x2 - x1, 2)
        } else {
            return (x1 - x2, 1)
        }
    }()
    if greaterOne == 1 {
        if v1 > v2 {
            return "NO"
        }
    } else if greaterOne == 2 {
        if v2 > v1 {
            return "NO"
        }
    }
    while(true) {
        currentLocation1 = currentLocation1 + v1
        currentLocation2 = currentLocation2 + v2
        if differenceInLocations == 0 {
            return "YES"
        }
        if greaterOne == 1 {
            if differenceInLocations > currentLocation1 - currentLocation2  && currentLocation1 - currentLocation2 >= 0 {
                differenceInLocations = currentLocation1 - currentLocation2
            } else {
                return "NO"
            }
        } else if greaterOne == 2 {
            if differenceInLocations > currentLocation2 - currentLocation1 && currentLocation2 - currentLocation1 >= 0{
                differenceInLocations = currentLocation2 - currentLocation1
            } else {
                return "NO"
            }
        }

    }

}