// Judges with GCC >= 12 only needs Ofast
// #pragma GCC optimize("O3,no-stack-protector,fast-math,unroll-loops,tree-vectorize")
// MLE optimization
// #pragma GCC optimize("conserve-stack")
// Old judges
// #pragma GCC target("sse4.2,popcnt,lzcnt,abm,mmx,fma,bmi,bmi2")
// New judges. Test with assert(__builtin_cpu_supports("avx2"));
// #pragma GCC target("avx2,popcnt,lzcnt,abm,bmi,bmi2,fma,tune=native")
// Atcoder
// #pragma GCC target("avx2,popcnt,lzcnt,abm,bmi,bmi2,fma")
/*
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> ordered_set;
- insert(x),erase(x)
- find_by_order(k): return iterator to the k-th smallest element
- order_of_key(x): the number of elements that are strictly smaller
*/
#include<bits/stdc++.h>
using namespace std;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
uniform_real_distribution<> pp(0.0,1.0);
#define int long long
#define ld long double
#define pii pair<int,int>
#define piii pair<int,pii>
#define mpp make_pair
#define fi first
#define se second
const int inf=1e18;
const int mod=998244353;
const int maxn=500005;
const int bl=650;
const int maxs=655;
const int maxm=200005;
const int maxq=1000005;
const int maxl=25;
const int maxa=1000000;
const int root=3;
int power(int a,int n){
int res=1;
while(n){
if(n&1) res=res*a%mod;
a=a*a%mod;n>>=1;
}
return res;
}
const int iroot=power(3,mod-2);
const int base=101;
int n,T;
void solve(){
cin >> n >> T;
vector<int> a(n);
for(int i=0;i<n;i++){
cin >> a[i];
a[i]%=T;
}
sort(a.begin(),a.end());
a.erase(unique(a.begin(),a.end()),a.end());
n=(int)a.size();
int l=0,r=T/2-1,res=T/2;
auto check = [&](int d){
deque<int> dl,dr;
int cnt=0;
//cout << "*" << d << '\n';
for(int i=0;i<n;i++){
int l=(a[i]-d+T)%T,r=(a[i]+d)%T;
if(l>r) cnt++;
dl.push_back(l);dr.push_back(r+1);
//cout << l << ' ' << r << '\n';
}
//cout << cnt << '\n';
while(dl.front()>dl.back()) dl.push_back(dl.front()),dl.pop_front();
while(dr.front()>dr.back()) dr.push_back(dr.front()),dr.pop_front();
//for(int x:dl) cout << x << ' ';
//cout << '\n';
//for(int x:dr) cout << x << ' ';
//cout << '\n';
if(cnt==n) return true;
int pos=0;
for(int x:dl){
while(pos<(int)dr.size() && dr[pos]<=x) cnt--,pos++;
cnt++;
if(cnt==n) return true;
}
return false;
};
while(l<=r){
int mid=(l+r)>>1;
if(check(mid)) res=mid,r=mid-1;
else l=mid+1;
}
cout << res << '\n';
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);cout.tie(NULL);
int test=1;//cin >> test;
while(test--) solve();
}
