import std.algorithm, std.container, std.conv, std.math, std.range, std.typecons, std.stdio, std.string;

auto rdsp(){return readln.splitter;}
void pick(R,T)(ref R r,ref T t){t=r.front.to!T;r.popFront;}
void readV(T...)(ref T t){auto r=rdsp;foreach(ref v;t)pick(r,v);}
void readA(T)(size_t n,ref T[]t){t=new T[](n);auto r=rdsp;foreach(ref v;t)pick(r,v);}

void main()
{
  int n, x; readV(n, x);
  int[] a; readA(n, a);

  auto ans = 0L;
  foreach (i; 1..n) {
    if (a[i-1]+a[i] > x) {
      auto r = min(a[i], a[i-1]+a[i]-x);
      a[i] -= r;
      ans += r;

      if (a[i] == 0) {
        r = a[i-1]-x;
        ans += r;
      }
    }
  }

  writeln(ans);
}
