int n,m,s=0;
int main(){
    int f,b;
    cin>>n>>m;
    cin>>f;
    for(int i=1;i<=n-1;i++){
        cin>>b;
        if(f+b>m){
            s+=(f+b-m);
        }
        f=max(b-(f+b-m),0);
    }
    cout<<s<<endl;
    
    return 0;
}