#include<iostream>
using namespace std;
int main(){
    int k, n, arr[101],x=0;
    cin>>k>>n;

    for(int i=0; i<n; i++){
        cin>> arr[i];

    }
    for(int i=0;i<n;i++){

        if(k>=arr[i]){
            if(i != n-1){
                x = x + arr[i+1];
                arr[i+1] = x;

                x = 0;

            }
            else{
                x = 0;
            }


        }
        else{
            if(i != n-1){
                x = (arr[i]-k) + arr[i+1];
                arr[i+1] = x;


            }
            else{
                x = arr[i] - k;
            }
        }
    //    printf("X : %d\n",x);
    }
    if(x<=0)
    cout<<0;
    else
    cout<<x;

}