#include<bits/stdc++.h>
using namespace std;
const int N = 1e7 + 10;
long long n, x;
long long a[N];
long long ans;
int main() {
	scanf("%lld%lld", &n, &x);
	for (long long i = 1; i <= n; ++i) {
		scanf("%lld", &a[i]);
	}
	for (long long i = 1; i <= n - 1; ++i) {
		if (a[i] + a[i + 1] > x) {
			long long d = a[i] + a[i + 1] - x;
			if (a[i + 1] >= d) {
				a[i + 1] -= d;
			} else {
				d -= a[i + 1];
				a[i + 1] = 0;
				a[i] -= d;
			}
			ans += d;
		}
	}
	printf("%lld", ans);
	return 0;
}