#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
  int N;
  cin>>N;
  vector<int> S(N);
  for(int i=0;i<N;i++) cin>>S[i];
  int ans = 1e9;
  sort(S.begin(),S.end());
  for(int i=1;i<N;i++)if(S[i] != S[i-1]) ans = min(ans,S[i]-S[i-1]);
  if(ans != 1e9) cout<<ans<<endl;
  else cout<<-1<<endl;
}