Problem:
Toggling Cases

Write a program which converts uppercase/lowercase letters to lowercase/uppercase for a given string.

Input

A string is given in a line.

Output

Print the converted string in a line. Note that you do not need to convert any characters other than alphabetical letters.

Constraints

The length of the input string < 1200

Sample Input

fAIR, LATER, OCCASIONALLY CLOUDY.

Sample Output

Fair, later, occasionally cloudy.

Solution in C# (judge verdict: Wrong Answer)

using System;

namespace AOJ.ITP
{
    public class TogglingCases
    {
        public static void Main()
        {
            string input = Console.ReadLine();
            string output = "";
            for (int i = 0; i < input.Length; i++)
            {
                if (input[i] >= 'a' && input[i] <= 'z') { output += input.Substring(i, 1).ToUpper(); }
                else if (input[i] >= 'A' && input[i] <= 'Z') { output += input.Substring(i, 1).ToLower(); }
                else { output += input.Substring(i, 0); }
            }
            Console.WriteLine(output);
        }
    }
}