# include<bits/stdc++.h>
using namespace std;
const int N = 10e5 + 5;
long long m[N], n, x, ans;
int main(){
	cin >> n >> x;
	for(int i = 1; i <= n; i++)
		cin >> m[i];
	for(int i = 2; i <= n; i++)
		if(m[i - 1] + m[i] > x) ans += (m[i] + m[i - 1] - x), m[i] -= (m[i] + m[i - 1] - x);
	cout << ans;
	return 0;
} 

第二次发帖，希望有大佬指出错误，谢谢