using System;
using System.Linq;
using System.Collections.Generic;

namespace Contest
{
    class Program
    {
        static void Main(string[] args)
        {
            ARC064.C();
        }
        class ARC064
        {
            public static void C()
            {
                var N = Read.Int();
                var X = Read.Long();
                var A = Read.LongN();

                long count = 0;
                if (A[0] > X) { count += A[0] - X;A[0] = X; }
                for(int i = 1; i < N; ++i)
                {
                    if (A[i] + A[i - 1] > X)
                    {
                        count += A[i] + A[i - 1] - X;
                        A[i] = X - A[i - 1];
                    }
                }
                Console.WriteLine(count);
            }
            public static void D()
            {
                var S = Read.Str();
                var N = S.Length;
                Console.WriteLine(S[0] == S[N - 1] ^ N % 2 > 0 ? "First" : "Second");
            }
            public static void E()
            {
                var XS = Read.Long();
                var YS = Read.Long();
                var XT = Read.Long();
                var YT = Read.Long();
                var N = Read.Int();
                var XYR = Enumerable.Range(0, N).Select(i => Read.LongN()).ToList();
                XYR.Add(new long[] { XS, YS, 0 });
                XYR.Add(new long[] { XT, YT, 0 });
                var Adj = new Dictionary<int, Dictionary<int, double>>();
                for(int i = 0; i < N + 2; ++i)
                {
                    Adj.Add(i, new Dictionary<int, double>());
                }
                Func<long, long, long, long, double> calcDist = (x1, y1, x2, y2) =>
                {
                    double dx = x1 - x2, dy = y1 - y2;
                    return Math.Sqrt(dx * dx + dy * dy);
                };
                for (int i = 0; i < N+2; ++i)
                {
                    for(int j = i + 1; j < N + 2; ++j)
                    {
                        var d = Math.Max(0, calcDist(XYR[i][0], XYR[i][1], XYR[j][0], XYR[j][1]) - XYR[i][2] - XYR[j][2]);
                        Adj[i].Add(j, d);
                        Adj[j].Add(i, d);
                    }
                }
                var dist = Util.DijkstraDouble(Adj, N + 2, (N + 2) * (N + 1) / 2, N);
                Console.WriteLine(dist[N + 1]);
            }
        }
        class Util
        {
            public class PriorityQueue<T> where T : IComparable
            {
                private IComparer<T> _comparer = null; private bool _isAsc = true; private T[] _heap; private int _sz = 0;
                public PriorityQueue(int maxSize, IComparer<T> comparer) { _heap = new T[maxSize]; _comparer = comparer; }
                public PriorityQueue(int maxSize, bool isAsc = true) { _heap = new T[maxSize]; _isAsc = isAsc; }
                private int Compare(T x, T y) { if (_comparer != null) { return _comparer.Compare(x, y); } return _isAsc ? x.CompareTo(y) : y.CompareTo(x); }
                public void Push(T x) { var i = _sz++; while (i > 0) { var p = (i - 1) / 2; if (Compare(_heap[p], x) <= 0) { break; } _heap[i] = _heap[p]; i = p; } _heap[i] = x; }
                public T Pop() { T ret = _heap[0]; T x = _heap[--_sz]; int i = 0; while (i * 2 + 1 < _sz) { int a = i * 2 + 1; int b = i * 2 + 2; if (b < _sz && Compare(_heap[b], _heap[a]) < 0) { a = b; } if (Compare(_heap[a], x) >= 0) { break; } _heap[i] = _heap[a]; i = a; } _heap[i] = x; return ret; }
                public int Count() { return _sz; }
                public T Peek() { return _heap[0]; }
                public bool Contains(T x) { for (int i = 0; i < _sz; i++) if (x.Equals(_heap[i])) return true; return false; }
            }
            public class MyTuple<T1, T2> : IComparable where T1 : IComparable<T1>
            {
                public readonly T1 Item1; public readonly T2 Item2;
                public MyTuple(T1 item1, T2 item2) { Item1 = item1; Item2 = item2; }
                public int CompareTo(object obj) { return Item1.CompareTo(((MyTuple<T1, T2>)obj).Item1); }
            }
            public static double[] DijkstraDouble(Dictionary<int, Dictionary<int, double>> adj, int N, int M, int start)
            {
                double INF = 1e20;
                var dist = Enumerable.Range(0, N + 1).Select(i => INF).ToArray();
                var queue = new PriorityQueue<MyTuple<double, int>>(N + M + 100);
                dist[start] = 0;
                queue.Push(new MyTuple<double, int>(0, start));
                while (queue.Count() > 0)
                {
                    var kvp = queue.Pop();
                    var d = kvp.Item1; var v = kvp.Item2;
                    if (dist[v] < d) { continue; }
                    foreach (var kvp2 in adj[v])
                    {
                        var newV = kvp2.Key;
                        var newD = dist[v] + kvp2.Value;
                        if (newD < dist[newV])
                        {
                            dist[newV] = newD;
                            queue.Push(new MyTuple<double, int>(newD, newV));
                        }
                    }
                }
                return dist;
            }
        }

        static class Read
        {
            static Queue<string> queue = new Queue<string>();
            static void Enqueue() { var ss = Console.ReadLine().Split(' '); foreach (var s in ss) { queue.Enqueue(s); } }
            public static int Int() { if (queue.Count == 0) { Enqueue(); } return Convert.ToInt32(queue.Dequeue()); }
            public static long Long() { if (queue.Count == 0) { Enqueue(); } return Convert.ToInt64(queue.Dequeue()); }
            public static string Str() { if (queue.Count == 0) { Enqueue(); } return queue.Dequeue(); }
            public static int[] IntN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToInt32(s)).ToArray(); }
            public static long[] LongN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToInt64(s)).ToArray(); }
            public static ulong[] ULongN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToUInt64(s)).ToArray(); }
            public static string[] StrN() { return Console.ReadLine().Split(' '); }
            public static Tuple<int, int>[] TupleInt(int n) { List<Tuple<int, int>> list = new List<Tuple<int, int>>(); for (int i = 0; i < n; ++i) { var ab = Read.IntN(); list.Add(new Tuple<int, int>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<long, long>[] TupleLong(int n) { List<Tuple<long, long>> list = new List<Tuple<long, long>>(); for (int i = 0; i < n; ++i) { var ab = Read.LongN(); list.Add(new Tuple<long, long>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<string, string>[] TupleStr(int n) { List<Tuple<string, string>> list = new List<Tuple<string, string>>(); for (int i = 0; i < n; ++i) { var ab = Read.StrN(); list.Add(new Tuple<string, string>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<double, double>[] TupleDouble(int n) { List<Tuple<double, double>> list = new List<Tuple<double, double>>(); for (int i = 0; i < n; ++i) { var ab = Read.LongN(); list.Add(new Tuple<double, double>(ab[0], ab[1])); } return list.ToArray(); }
            public static long[,] LongMatrix(int r, int c)
            {
                var mat = new long[r, c];
                for (int i = 0; i < r; ++i)
                {
                    var x = Read.LongN();
                    for (int j = 0; j < c; ++j)
                    {
                        mat[i, j] = x[j];
                    }
                }
                return mat;
            }
            public static Dictionary<int, HashSet<int>> AdjacencyList(int N, int M, bool isDirectional = false)
            {
                Dictionary<int, HashSet<int>> dict = new Dictionary<int, HashSet<int>>();
                for (int i = 0; i <= N; ++i) { dict.Add(i, new HashSet<int>()); }
                for (int i = 0; i < M; ++i)
                {
                    var ab = Read.IntN(); dict[ab[0]].Add(ab[1]);
                    if (!isDirectional) { dict[ab[1]].Add(ab[0]); }
                }
                return dict;
            }
            public static Dictionary<int, Dictionary<int, long>> AdjacencyListWithWeight(int N, int M)
            {
                Dictionary<int, Dictionary<int, long>> dict = new Dictionary<int, Dictionary<int, long>>();
                for (int i = 0; i <= N; ++i)
                {
                    dict.Add(i, new Dictionary<int, long>());
                }
                for (int i = 0; i < M; ++i)
                {
                    var ab = Read.IntN();
                    dict[ab[0]].Add(ab[1], ab[2]);
                    dict[ab[1]].Add(ab[0], ab[2]);
                }
                return dict;
            }
        }
    }
}


Measured memory_bytes: 29660