static void Main(string[] args) {
            int[] frequency1 = new int[26];
            var s = reader.ReadLine();
            int[] frequency2 = new int[s.Length + 1];
            int diffChars = 0;
            foreach (char c in s) {
                int ci = c - 'a';
                frequency2[frequency1[ci]]--;
                frequency1[ci]++;
                if (frequency1[ci] == 1) {
                    diffChars++;
                }
                frequency2[frequency1[ci]]++;
            }
            int minF2I = int.MaxValue;
            int maxF2I = int.MinValue;
            foreach (int fq in frequency1) {
                if (fq == 0)
                    continue;
                minF2I = Math.Min(minF2I, fq);
                maxF2I = Math.Max(maxF2I, fq);
            }
            if (maxF2I == minF2I || minF2I == 1 && frequency2[maxF2I] == diffChars - 1 || (maxF2I - minF2I == 1 && frequency2[maxF2I] == 1)) {
                writer.Write("YES");
            }
            else {
                writer.Write("NO");
            }
            writer.Flush();
            writer.Close();
        }