#include<bits/stdc++.h>
using namespace std;
int main(){
int n,max1;
long long sum=0; 
cin>>n>>max1;
int s1[n+10];
	for(int s=1;s<=n;s++){
		scanf("%d",&s1[s]);
	} 
	for(int s=1;s<n;s++){
		if(s1[s]+s1[s+1]>max1){
			int x=s1[s],y=s1[s+1];
			while(x+y>max1){
				if(y>0)
					y--;
				else
					x--;	
			}
			sum+=s1[s]-x+s1[s+1]-y;
			s1[s]=x;
			s1[s+1]=y;
		}	
	}
		printf("%lld",sum);
	return 0;
}