#include <bits/stdc++.h>

using namespace std;

#define maxn 100005

#define ll long long

ll ai[maxn],n,m,ans;

inline void in(ll &now)

{

    char Cget=getchar();now=;

    while(Cget>''||Cget<'')Cget=getchar();

    while(Cget>=''&&Cget<='')

    {

        now=now*+Cget-'';

        Cget=getchar();

    }

}

int main()

{

    in(n),in(m);

    for(ll i=;i<=n;i++)

    {

        in(ai[i]);

        if(ai[i]+ai[i-]>m)

        {

            ans+=ai[i]+ai[i-]-m;

            ai[i]-=ai[i]+ai[i-]-m;

        }

    }

    cout<<ans;

    return ;

}