#include<bits/stdc++.h>
using namespace std;
int n,x,ans,d;
int  a[100009];
int main()
{
    scanf("%d%d",&n,&x);
    for(int i=1;i<=n-1;++i)
    {
        scanf("%d",&a[i]);
        if(a[i]+a[i-1]>x) 
        {
            d=(a[i]+a[i-1])-x;
            a[i]-=d;
            ans+=d;
        }
    }
    cout<<ans;
    return 0;
}