#include<bits/stdc++.h>
using namespace std;
const long long MaxN = 1e5 + 5;
long long n,k;
long long a[MaxN];
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
if(fopen("ANTS.inp","r"))
{
freopen("ANTS.inp","r",stdin);
freopen("ANTS.out","w",stdout);
}
cin >> n >> k;
for (long long i=1; i<=n; i++)
{
cin >> a[i];
}
long long ans = 0;
for (long long i=1; i<=n; i++)
{
if(a[i]<0)
{
ans=max(ans,abs(a[i]));
}
else
{
ans=max(ans,k-a[i]);
}
}
cout << ans;
}
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