#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll n,x,a[100010],cnt; 
int main(){
	cin>>n>>x;
	for(int i=1;i<=n;i++) cin>>a[i];
	for(int i=1;i<n;i++){
		if(a[i]+a[i+1]<=x) continue;
		ll f=a[i+1];
		cnt+=a[i]+f-x;
		if(a[i+1]>=cnt) a[i+1]-=cnt;
		else{
			a[i]-=cnt-a[i+1];
			a[i+1]=0;
		}
	}
	cout<<cnt;
	return 0;
}