Problem:
Score : 100 points

Problem Statement

A Hitachi string is a concatenation of one or more copies of the string hi.

For example, hi and hihi are Hitachi strings, while ha and hii are not.

Given a string S, determine whether S is a Hitachi string.

Constraints

The length of S is between 1 and 10 (inclusive).

S is a string consisting of lowercase English letters.

Input

Input is given from Standard Input in the following format:

S

Output

If S is a Hitachi string, print Yes; otherwise, print No.

Sample Input 1

hihi

Sample Output 1

Yes

hihi is the concatenation of two copies of hi, so it is a Hitachi string.

Sample Input 2

hi

Sample Output 2

Yes

Sample Input 3

ha

Sample Output 3

No

Solution in C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using static System.Console;
using static System.Math;

namespace Atcoder
{
    class Program
    {
        static StreamWriter sw = new StreamWriter(OpenStandardOutput()) { AutoFlush = false };
        static void Main(string[] args)
        {
            try
            {
                SetOut(sw);
                Solve.Answer();
                Out.Flush();
            }
            catch (Exception ex)
            {
                WriteLine(ex.ToString());
            }
        }
    }

    public class Solve
    {
        public static void Answer()
        {
            var s = ReadLine();
            for (int i = 0; i < s.Length; i++)
            {
                if (i % 2 == 0)
                {
                    if (s[i] != 'h')
                    {
                        WriteLine("No");
                        return;
                    }
                }
                else
                {
                    if (s[i] != 'i')
                    {
                        WriteLine("No");
                        return;
                    }
                }
            }
            if (s.Length == 1) WriteLine("No");
            if (s.Length == 1) return;
            WriteLine("Yes");
        }

        public class IO
        {
            #region Input
            public static int RInt => int.Parse(ReadLine());
            public static long RLong => long.Parse(ReadLine());
            public static double RDouble => double.Parse(ReadLine());

            public static string[] RSString => ReadLine().Split();
            public static int[] RSInt => ReadLine().Split().Select(s => int.Parse(s)).ToArray();
            public static long[] RSLong => ReadLine().Split().Select(s => long.Parse(s)).ToArray();
            public static double[] RSDouble => ReadLine().Split().Select(s => double.Parse(s)).ToArray();
            #endregion

            #region Output
            public static void OutJoinSpace<T>(IEnumerable<T> list) => WriteLine(string.Join(" ", list));
            public static void WriteLineYes_or_No(bool flag) => WriteLine(flag ? "Yes" : "No");
            public static void WriteLineYES_or_NO(bool flag) => WriteLine(flag ? "YES" : "NO");
            #endregion
        }

        public class Mod
        {
            #region
            private readonly static long M = 1000000007;

            public static long Add(long a, long b) => (a * b) % M;
            public static long Sub(long a, long b) => (a - b) % M >= 0 ? (a - b) % M : (a - b) % M + M;
            public static long Multi(long a, long b) => (a * b) % M;
            #endregion
        }
    }
}