#include<bits/stdc++.h>
using namespace std;
long long n, x, ans, a[1000010];
int main() {
	cin >> n >> x;
	for (int i = 0; i < n; i++) {
		cin >> a[i];
	}
	for (int i = 1; i < n; i++) {
		if (a[i - 1] + a[i] > x) {
			ans += a[i - 1] + a[i] - x;
			a[i] -= a[i - 1] + a[i] - x;
		}
	}
	cout << ans;
	return 0;
}