def result(n):
n=str(n)
m=n.find(".")
if m==-1:
n+="."
m=0
for i in range(m,10):
n+="0"
return n
def count(a ,arr):
n=0
for i in range(len(arr)):
if arr[i]==a:
n+=1
if arr[i]>a:
return n
return n
inp=input()
inp=inp.split(" ")
n=int(inp[0])
l=int(inp[1])
inp2=input()
inp2=inp2.split(" ")
inp2=[int(x) for x in inp2]
inp2.sort()
max=0
i_f=0
i_l=0
if inp2[0]>l-inp2[n-1]:
max=inp2[0]*2
else:
max=(l-inp2[n-1])*2
for i in range(n-1):
if int(inp2[i+1])-int(inp2[i])>max:
max=int(inp2[i+1])-int(inp2[i])
i_f=inp2[i]
i_l=inp2[i+1]
if n==1:
if inp2[0]==0 or inp2[0]==l:
max=l*2
else:
if inp2[0]>l-inp2[0]:
max=inp2[0]*2
else:
max=(l-inp2[0])*2
i_f=inp2[0]
i_l=inp2[0]
if l-int(inp2[n-1])>max/2 and n!=1:
if n==2:
if int(inp2[1])-int(inp2[0])>0:
max=(l-int(inp2[n-1]))*2
m=(count(i_f,inp2))
k=count(i_l,inp2)
print(result(max/(2)))#include <iostream>
#include <bits/stdc++.h>
using namespace std;
#define PB push_back
#define INF (int)1e9
#define PI 3.1415926535897932384626433832795
#define MOD 1000000007
#define ll long long
#define F first
#define S second
#define All(x) x.begin(), x.end()
#define Sort(x) sort(All(x))
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
ll n, l;
cin>>n>>l;
vector<double> a(n);
for(ll i=0; i<n; i++)
cin>>a[i];
Sort(a);
double md=0;
for(ll i=0; i<n-1; i++)
md=max(md, a[i+1]-a[i]);
double x=0, y=0;
if(a[0]!=0)
x=a[0]-0;
if(a[n-1]!=l)
y=l-a[n-1];
cout<<fixed << setprecision(9)<<max(md/2, max(x, y))<<endl;
return 0;
}
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