#include <bits/stdc++.h>
using namespace std;
template <typename T1, typename T2>
void chkmin(T1 &x, T2 y) {
  if (x > y) x = y;
}
template <typename T1, typename T2>
void chkmax(T1 &x, T2 y) {
  if (x < y) x = y;
}
inline void debug(int x) { fprintf(stderr, "ycx has aked ioi %d times\n", x); }
namespace fastio {
char rbuf[1 << 23], *p1 = rbuf, *p2 = rbuf, wbuf[1 << 23], *p3 = wbuf;
inline char getc() {
  return p1 == p2 &&
                 (p2 = (p1 = rbuf) + fread(rbuf, 1, 1 << 23, stdin), p1 == p2)
             ? -1
             : *p1++;
}
inline void putc(char x) { (*p3++ = x); }
template <typename T>
void read(T &x) {
  x = 0;
  char c = getchar();
  T neg = 0;
  while (!isdigit(c)) neg |= !(c ^ '-'), c = getchar();
  while (isdigit(c)) x = (x << 3) + (x << 1) + (c ^ 48), c = getchar();
  if (neg) x = (~x) + 1;
}
template <typename T>
void recursive_print(T x) {
  if (!x) return;
  recursive_print(x / 10);
  putc(x % 10 ^ 48);
}
template <typename T>
void print(T x) {
  if (!x) putc('0');
  if (x < 0) putc('-'), x = ~x + 1;
  recursive_print(x);
}
template <typename T>
void print(T x, char c) {
  if (!x) putc('0');
  if (x < 0) putc('-'), x = ~x + 1;
  recursive_print(x);
  putc(c);
}
void print_final() { fwrite(wbuf, 1, p3 - wbuf, stdout); }
}  // namespace fastio
const int MAXN = 1e5;
const int INF = 0x3f3f3f3f;
int n, a[MAXN + 5], b[MAXN + 5], l[MAXN + 5], r[MAXN + 5];
int stk[MAXN + 5], tp;
int main() {
  scanf("%d", &n);
  for (int i = 0; i <= n + 1; i++) scanf("%d", &a[i]);
  for (int i = 1; i <= n; i++) scanf("%d", &b[i]);
  b[0] = b[n + 1] = r[0] = l[n + 1] = INF;
  stk[tp = 1] = 0;
  for (int i = 1; i <= n + 1; i++) {
    while (tp && a[stk[tp]] + r[stk[tp]] < a[i]) --tp;
    r[i] = (b[i] << 1) - (a[i] - a[stk[tp]]);
    if (r[i] > 0) {
      while (tp && a[stk[tp]] + r[stk[tp]] <= a[i] + r[i]) --tp;
      stk[++tp] = i;
    }
  }
  stk[tp = 1] = n + 1;
  for (int i = n; ~i; i--) {
    while (tp && a[stk[tp]] - l[stk[tp]] > a[i]) --tp;
    l[i] = (b[i] << 1) - (a[stk[tp]] - a[i]);
    if (l[i] > 0) {
      while (tp && a[stk[tp]] - l[stk[tp]] >= a[i] - l[i]) --tp;
      stk[++tp] = i;
    }
  }
  stk[tp = 1] = 0;
  int ans = INF;
  for (int i = 1; i <= n; i++)
    if (0ll + l[i] + r[i] >= (b[i] << 1)) return puts("0") & 0;
  for (int i = 1; i <= n + 1; i++) {
    if (l[i] > 0) {
      int L = 1, R = tp, p = -1;
      while (L <= R) {
        int mid = L + R >> 1;
        if (a[stk[mid]] + r[stk[mid]] < a[i] - l[i])
          R = mid - 1;
        else
          p = mid, L = mid + 1;
      }
      chkmin(ans, a[i] - a[stk[p]]);
    }
    if (r[i] > 0) {
      while (tp && a[stk[tp]] + r[stk[tp]] <= a[i] + r[i]) --tp;
      stk[++tp] = i;
    }
  }
  printf("%d.%d\n", ans >> 1, 5 * (ans & 1));
  return 0;
}
