#include<bits/stdc++.h>
using namespace std;
const long long N=1e8+3;
long long s[N];
int main()
{
int a,b,ans;
cin>>a>>b;
for(int i=1;i<=a;++i)
{
cin>>s[i];
if(s[i]+s[i-1]>b)ans+=s[i]+s[i-1]-b,s[i]=s[i]-(s[i]+s[i-1]-b);
}
cout<<ans;
return 0;
}