Submission #1442952

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Source Code Expand

using System;
using System.Linq;

namespace ABC056C
{
    class Program
    {
        static void Main(string[] args)
        {
            new Solver().Solve();
        }
    }

    class Solver
    {
        int X;

        public void Solve()
        {
            // キャスト前の値以上の整数なら条件を満たす.
            int ans = (int)((-1.0 + Math.Sqrt(1 + 8 * X)) / 2.0);

            // 条件を満たすときtrueを返す.
            Func<int, bool> check = t => t * t + t - 2 * X >= 0;
            if (!check(ans))
            {
                ans++;
            }
            Console.WriteLine(ans);
        }

        public Solver()
        {
            X = ReadInt();
        }

        static String ReadString() { return Console.ReadLine(); }
        static int ReadInt() { return int.Parse(Console.ReadLine()); }
        static long ReadLong() { return long.Parse(Console.ReadLine()); }
        static double ReadDouble() { return double.Parse(Console.ReadLine()); }
        static String[] ReadStringArray() { return Console.ReadLine().Split(' '); }
        static int[] ReadIntArray() { return Console.ReadLine().Split(' ').Select(e => int.Parse(e)).ToArray(); }
        static long[] ReadLongArray() { return Console.ReadLine().Split(' ').Select(e => long.Parse(e)).ToArray(); }
        static double[] ReadDoubleArray() { return Console.ReadLine().Split(' ').Select(e => double.Parse(e)).ToArray(); }
    }

}

Submission Info

Judge Result