#include <iostream>
using namespace std;
#define int long long
signed main() {
	int n,x,sum=0;
	cin>>n>>x;
	int a[n+1];
	cin>>a[1];
	if(a[1]>x){
		sum+=x-a[1];
		a[1]=x;
	}
	for(int i=2;i<=n;i++){
		cin>>a[i];
		if(a[i]+a[i-1]>x){
			sum+=a[i]+a[i-1]-x;
			a[i]=x-a[i-1];
		}
	}    
	cout<<sum;
    return 0;
}