#include <bits/stdc++.h>
#define ll long long
#define inf int(1e8)
#define lnf ll(1e18)
#define pair<int,int> pii;
#define fastio ios::sync_with_stdio(false),cin.tie(0)
using namespace std;
vector<ll> vec;
ll n, tar;

int SUM (ll target) {
	ll sum = 0;
	for (auto it : vec) {
		if (tar < it + target) sum += it + target - tar;
		if (sum > target) return 0;
	}
	if (sum == target) return 2;
	return 1;
}

void solve(){
	
	cin >> n;
	cin >> tar;
	vec.resize(n-1);
	int times = 0;
	for (int i = 0 ; i < n - 1; i++) cin >> vec[i];
	for (auto it : vec) {
		if (it == tar) times ++;
	}
	if (times >= 2) {
		cout << 0 << '\n';
		return;
	}
	ll l = 1, r = 1e17;
	while (l < r) {
		ll mid = (l + r + 1)/2;
		if (SUM(mid)) l = mid;
		else r = mid - 1;
	}
	ll mid = (l + r)/2;
	ll ans;
	ll k = 1;
	for (ll i = max(k,mid - 10); i <= mid + 10 ; i++) {
		if (SUM(i) == 2){
			cout << i << '\n';
			return ;
		}else if(SUM(i) == 1){
			ans = i;
		}else break;
	}
	cout << ans << '\n';
}

int main(void) {
	fastio;
	solve();		
}