Codility Lesson 3-2 Time Complexity

FrogJmp.cs

using System;
// you can also use other imports, for example:
// using System.Collections.Generic;

// you can write to stdout for debugging purposes, e.g.
// Console.WriteLine("this is a debug message");

class Solution {
    public int solution(int X, int Y, int D) {
        if ((Y - X) < D && Y != X) return 1;
        
		var r = (double)( (Y - X) + ((Y-X)%D) ) / D;
			
		return (int)Math.Ceiling(r);
        
        // write your code in C# 6.0 with .NET 4.5 (Mono)
    }
}