#include<bits/stdc++.h>
#define ing long long
using namespace std;
const int maxn=2e5+5; 
int n,x;
int a[maxn];
int ans;
signed main()
{
	cin>>n>>x;
	for(int i=1; i<=n; i++)
		cin>>a[i];
	for(int i=2; i<=n; i++)
	{
		if(a[i]+a[i-1] > x)
		{
			if(a[i]+a[i-1]-x > a[i])
			{
				ans+=a[i];
				a[i]=0;
				ans+=(a[i-1]-x);
				a[i-1]-=(a[i-1]-x);
			}
			else
			{
				ans+=(a[i]+a[i-1]-x);
				a[i]-=(a[i]+a[i-1]-x);
			}
		}
	}
	cout<<ans;
	return 0;
}