#include<bits/stdc++.h>
using namespace std;
const int N=1e6+10;
int a[N];
int main(){
	long long n,x;
	cin>>n>>x;
	for(int i=1;i<=n;i++)
		cin>>a[i];
	int sum=0;
	for(int i=1;i<=n;i++){
		if(a[i]+a[i-1]>x)
			sum+=a[i]+a[i-1]-x;
		else if(a[i]+a[i+1]>x)
			sum+=a[i]+a[i+1]-x;
	}
	cout<<(sum-1)/2;
}