#include <bits/stdc++.h>
using namespace std;
using lf = double;
const int N = 5010;
int n, a;
int s[N];
int l[N], r[N];
int main() {
	scanf("%d%d", &n, &a);
	for (int i = 1; i <= n + 1; ++i)
		scanf("%d", &s[i]);
	for (int i = 1; i <= n + 1; ++i)
		scanf("%d%d", &l[i], &r[i]);
	lf t = 0, v = 0;
	for (int i = 2; i <= n + 1; ++i) {
		lf v1 = sqrt(v * v + 2 * a * (s[i] - s[i - 1]));
		lf tp = (v1 - v) / a;
		if (t + tp > r[i]) {
			puts("kaibai");
			return 0;
		}
		if (t + tp > l[i]) {
			t += tp;
			v = v1;
			continue;
		}
		if (0.5 * a * (l[i] - t) * (l[i] - t) >= s[i] - s[i - 1])
			v = sqrt(2 * a * (s[i] - s[i - 1]));
		else 
			v = (s[i] - s[i - 1] + 0.5 * a * (l[i] - t) * (l[i] - t)) / (l[i] - t);
		t = l[i];
	}
	printf("%.8lf", t);
	return 0;
}