#include <cstring>
#include <iostream>
#include <algorithm>
#include <cmath>
using namespace std;

#define inf 0x3f3f3f3f
#define endl '\n'
#define x first
#define y second
#define int long long

const int N = 1e6 + 10;
const int mod = 1e9 + 7;

typedef pair<int, int> PII;
typedef long long LL;
typedef unsigned long long ULL;
int a[N];

int w[N];
int id[N];
int cnt;
void solve()
{
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++)
    {
        cin >> a[i];
    }

    if (a[1] <= a[2])
    {
        cnt++;
        id[cnt] = 1;
        w[cnt] = a[1];
    }
    for (int i = 2; i < n; i++)
    {
        if (a[i] < a[i - 1] && a[i] < a[i + 1])
        {
            cnt++;
            id[cnt] = i;
            w[i] = a[i];
        }
    }
    if (a[n] <= a[n - 1])
    {
        cnt++;
        id[cnt] = n;
        w[n] = a[n];
    }
    int ans = 0;
    for (int i = 2; i < n; i++)
    {
        if (a[i] >= a[i - 1] && a[i] >= a[i + 1])
        {
            int l = 1, r = cnt;
            while (l < r)
            {
                int mid = l + r >> 1;
                if (id[mid] >= i)
                    r = mid;
                else
                    l = mid + 1;
            }
            int rr = id[l];

            l = 1, r = cnt;
            while (l < r)
            {
                int mid = (l + r + 1) >> 1;
                if (id[mid] <= i)
                    l = mid;
                else
                    r = mid - 1;
            }
            int ll = id[l];
            if (a[i] >= w[ll] && a[i] >= w[rr])
            {
                int tot = fmin(a[i] - w[ll], a[i] - w[rr]);
                ans = fmax(ans, tot);
            }
        }
    }
    cout << ans << endl;
}
signed main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int t = 1;
    while (t--)
        solve();
    return 0;
}