#include <cstdio>
long long cnt;
int main()
{
	int n, x, a, b;
	scanf("%d %d %d", &n, &x, &a);
	for (int i = 1; i < n; i++)
	{
		scanf("%d", &b);
		if (a + b > x)
			cnt += a + b - x, b = x - a; //优先考虑b
		if (a + b > x)
		    cnt += x - b, b = x - b;
		a = b;
	}
	printf("%d", cnt);
	return 0;
}