#include <bits/stdc++.h>
using namespace std;

signed main(){
    int n;cin>>n;
    vector<int> v(n);
    for(int i=0;i<n;i++)cin>>v[i];
    sort(v.begin(),v.end());
    int ans=1e9;
    for(int i=1;i<n;i++){
        if(v[i]==v[i-1])continue;
        ans=min(ans,v[i]-v[i-1]);
    }
    if(ans>1e8)cout<<-1<<endl;
    else cout<<ans<<endl;
}