#include<bits/stdc++.h>
using namespace std;
using ll = long long;
#define F first
#define S second
#define all(x) (x).begin(), (x).end()
template<typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &p)
{
return os << "(" << p.F << "," << p.S << ")";
}
template<typename T>
void print(const T &v, int lim = 1e9)
{
for(auto x : v)
if(lim-- > 0) cout << x << " ";
cout << "\n";
}
#define int long long
int N, T;
signed main()
{
ios::sync_with_stdio(0); cin.tie(NULL); cout.tie(NULL);
cin >> N >> T;
vector<int> a(N);
for(int &x : a) cin >> x;
int mn = 1e18;
for(int i = 0; i < T; i++)
{
// int i = 15;
int mx = 0;
for(int x : a)
{
int y = (x - i + T) % T;
mx = max(mx, min(y, T - y));
}
mn = min(mn, mx);
}
cout << mn << "\n";
}
