#include<bits/stdc++.h>
using namespace std;
const int maxn=1e5;
int a[maxn];
int n,m,ans;
int main()
{
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		cin>>a[i];
		while(a[i-1]+a[i]>m){
			a[i]--;
			ans++;
		}	
	}
	cout<<ans;
}