FrogRiverOne

        /// <summary>
        /// Solution
        /// 100/100
        /// </summary>
        /// <param name="X"></param>
        /// <param name="A"></param>
        /// <returns></returns>
        public static int solution(int X, int[] A)
        {
            bool[] flagArr = new bool[X];
            for (int i = 0; i < A.Length; i++)
            {
                if (flagArr[A[i] - 1] == false)
                {
                    flagArr[A[i] - 1] = true;
                    X--;
                }
                if (X == 0)
                {
                    return i;
                }
            }
            return -1;
        }