#include<bits/stdc++.h>
using namespace std;
#define task "a"
#define se second
#define fi first
#define ll long long
#define ii pair<ll, ll>
const long mxN = 5e5 + 7;
int n, dif, a[mxN];
bool Binary(int mid)
{
for (int i = 2; i <= n; i++)
{
if (a[i - 1] - mid <= a[i] - dif + mid)
return 1;
}
return a[1] + mid >= a[n] - mid;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
//freopen(task".INP", "r", stdin);
//freopen(task".OUT", "w", stdout);
cin >> n >> dif;
for (int i = 1; i <= n; i++)
cin >> a[i];
sort(a + 1, a + n + 1);
for (int i = 1; i <= n; i++)
a[i] -= (a[i] - a[1]) / dif * dif;
int l = 0, r = 1e9, ans = 1e9;
while (l <= r)
{
int mid = (l + r) / 2;
if (Binary(mid))
{
r = mid - 1;
ans = mid;
}
else
l = mid + 1;
}
cout << ans;
}
