#include <bits/stdc++.h>
using namespace std;
#define int long long
int32_t main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int n,t;
cin >> n >> t;
vector<int> arr(n+1);
vector<tuple<int,bool,int>> events;
for(int i=1;i<=n;i++) {
int a;cin>>a;
if(a>=t) {
a%=t;
events.emplace_back(0,!true,+a);
events.emplace_back(a,!false,+a);
events.emplace_back(a,!true,-a);
events.emplace_back(a+1+t/2,!false,-a);
events.emplace_back(a+1+t/2,!true,+a+t);
events.emplace_back(a+t,!false,+a+t);
events.emplace_back(a+t,!true,-(a+t));
} else {
events.emplace_back(0,!true,+a);
events.emplace_back(a,!false,+a);
events.emplace_back(a,!true,-a);
}
}
sort(events.begin(),events.end());
int negCnt = 0;
int posCnt = 0;
multiset<int> negSum,posSum;
int ans = 1e17;
for(int i = 0;i<events.size();i++) {
auto [position,typ,x] = events[i];
if(!typ) {
if(x>0) {
posCnt++;
posSum.insert(x);
} else {
negCnt++;
negSum.insert(x);
}
} else {
if(x>0) {
posCnt--;
posSum.erase(posSum.find(x));
} else {
negCnt--;
negSum.erase(negSum.find(x));
}
}
if(i==events.size()-1 or get<0>(events[i+1])!=position) {
if(!negSum.empty() and !posSum.empty()) {
int neg = *(--negSum.end());neg = -neg;
int pos = *(--posSum.end());
int newPosition = (neg+pos)/2;
if(newPosition<position)newPosition=position;
else if(i!=events.size()-1 and get<0>(events[i+1])<=newPosition)newPosition=get<0>(events[i+1])-1;
position = newPosition;
}
int negMax = 0;
if(!negSum.empty())negMax = position + *(--negSum.end());
int posMax = 0;
if(!posSum.empty())posMax = - position + *(--posSum.end());
ans=min(ans,max(posMax,negMax));
}
}
cout << ans << '\n';
}
