Exemple #1
0
        static void Main()
        {
            var ss = new StreamScanner(new StreamReader(Console.OpenStandardInput()));
            var sw = new StreamWriter(Console.OpenStandardOutput())
            {
                AutoFlush = false
            };

            new Program().Solve(ss, sw);
            sw.Flush();
        }
Exemple #2
0
        void Solve(StreamScanner ss, StreamWriter sw)
        {
            //---------------------------------
            var N = ss.Next(int.Parse);
            var A = ss.Next(long.Parse, N);

            if (A[0] != 0)
            {
                sw.WriteLine(-1);
                return;
            }

            var ans = 0L;

            for (var i = 1; i < N; i++)
            {
                if (A[i] > A[i - 1] + 1)
                {
                    sw.WriteLine(-1);
                    return;
                }

                if (A[i] == A[i - 1] + 1)
                {
                    continue;
                }
                if (A[i] <= A[i - 1])
                {
                    ans += A[i - 1];
                }
            }
            ans += A[N - 1];

            sw.WriteLine(ans);
            //---------------------------------
        }