#include<bits/stdc++.h>
using namespace std;
using Int = long long;
using Double = long double;
struct Precision{
  Precision(){
    cout<<fixed<<setprecision(12);
  }
}precision_beet;

//INSERT ABOVE HERE
signed main(){
  int n;
  cin>>n;
  vector<Double> a(n);
  for(int i=0;i<n;i++) cin>>a[i];

  auto calc=
    [&](Double x,bool f=0)->Double{
      auto v(a);
      for(int i=0;i<n;i++) v[i]-=i*x;
      Double b=0;
      for(int i=0;i<n;i++) b+=v[i];
      b/=n;
      Double c=0;
      for(int i=0;i<n;i++) c+=(v[i]-b)*(v[i]-b);
      if(f) cout<<b<<" "<<x<<endl;
      return c;
    };
  
  Double l=-1e9,r=1e9;
  for(int k=0;k<200;k++){
    Double m1=l+(r-l)/3;
    Double m2=l+(r-l)*2/3;
    if(calc(m1)<calc(m2)) r=m2;
    else l=m1;
  }
  Double c=calc(l,1);
  cout<<c<<endl;
  return 0;
}