#include<stdio.h>
int main()
{
	int n,s,i;
	long long sum=0;
	scanf("%ld",&n);
	scanf("%ld",&s);
	int a[100000];
	for(i=0;i<n;i++)
	   scanf("%ld",&a[i]);
	for(i=0;i<n-1;i++)
		if(a[i]+a[i+1]>s)
	    {	
	   	sum=sum+a[i]+a[i+1]-s;
	   	a[i+1]-=a[i]+a[i+1]-s;
	}
	printf("%d",sum);
	return 0;
 }