#include<bits/stdc++.h>     
using namespace std;
int arr[100000005];
int ans;
int main(){
	int n,m;
	cin>>n>>m;
	cin>>arr[1];
	for(int i=2;i<=n;i++){
		cin>>arr[i];
		if(arr[i]+arr[i-1]>m){
			int t=arr[i]+arr[i-1]-m;
			if(arr[i]<t){
				arr[i]=0;
				arr[i-1]-=t-arr[i];
				ans+=t;
			}else{
				arr[i]-=t;
				ans+=t;
			}
		}
	}
	cout<<ans;
	return 0;
}