codeforce - Vanya and Lanterns

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
int main()
{
    ll n,l;
    cin>>n>>l;
    ll ara[n+1];
    for(int i=0;i<n;i++)cin>>ara[i];
    sort(ara,ara+n);
    ll r= max(ara[0],l-ara[n-1])*2;
    for(int i=0;i<n-1;i++)
        r=max(r,ara[i+1]-ara[i]);
    cout.precision(20);
    cout<<fixed<<r/2.0<<endl;
}