#include <bits/stdc++.h>

#define FOR(i,a,b) for(int i= (a); i<((int)b); ++i)
#define RFOR(i,a) for(int i=(a); i >= 0; --i)
#define FOE(i,a) for(auto i : a)
#define ALL(c) (c).begin(), (c).end()
#define RALL(c) (c).rbegin(), (c).rend()
#define SUM(x) std::accumulate(ALL(x), 0LL)
#define MIN(v) *std::min_element(v.begin(), v.end())
#define MAX(v) *std::max_element(v.begin(), v.end())
#define EXIST(v,x) (std::find(v.begin(), v.end(), x) != v.end())
#define BIT_ON(bit, i) (((bit >> i) & 1) > 0)
#define BIT_COUNT(bit) (__builtin_popcount(bit))

typedef long long LL;
template<typename T> std::vector<T> make_v(size_t a){return std::vector<T>(a);}
template<typename T,typename... Ts> auto make_v(size_t a, Ts... ts){ return std::vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));}    // C++14
template<typename T,typename V> typename std::enable_if<std::is_class<T>::value==0>::type fill_v(T &t,const V &v){t=v;}
template<typename T,typename V> typename std::enable_if<std::is_class<T>::value!=0>::type fill_v(T &t,const V &v){for(auto &e:t) fill_v(e,v);}
template<class T> inline T ceil(T a, T b) { return (a + b - 1) / b; }
template<class T> inline void print(T x) { std::cout << x << std::endl; }
template<class T> inline void print_vec(const std::vector<T> &v) { for (int i = 0; i < v.size(); ++i) {  if (i != 0) {std::cout << " ";} std::cout << v[i];} std::cout << "\n"; }
inline bool inside(long long y, long long x, long long H, long long W) {return 0 <= y and y < H and 0 <= x and x < W; }
template<class T> inline double euclidean_distance(T y1, T x1, T y2, T x2) { return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)); }
template<class T> inline double manhattan_distance(T y1, T x1, T y2, T x2) { return abs(x1 - x2) + abs(y1 - y2); }
template<typename T> T &chmin(T &a, const T &b) { return a = std::min(a, b); }
template<typename T> T &chmax(T &a, const T &b) { return a = std::max(a, b); }

template<class T> inline std::vector<T> unique(std::vector<T> v) {
    sort(v.begin(), v.end());
    v.erase(unique(v.begin(), v.end()), v.end());
    return v;
}
// 初項s, 交差dのn個の数列の和
long long sum_of_arithmetic_progression(long long s, long long d, long long n) {
    return n * (2 * s + (n - 1) * d) / 2;
}

// 2のべき乗数かどうか
bool is_power_of_two(long long x) {
    return !(x & (x - 1));
}

// aとbの最大公約数 O(log min(a, b))
long long gcd(long long a, long long b) {
    if (b == 0) { return a; }
    return gcd(b, a % b);
}

// 数列vの最大公約数 O(N log d)
long long gcd(std::vector<long long> &v) {
    long long ans = v[0];
    for (int i = 1; i < (int)v.size(); ++i) {
        ans = gcd(ans, v[i]);
    }
    return ans;
}

// aとbの最小公倍数 O(log min(a, b))
long long lcm(long long a, long long b) {
    long long g = gcd(a, b);
    return a / g * b;
}

const int INF = 1u << 30u;
const long long LINF = 1ull << 60u;
const double EPS = 1e-9;
const long double PI = acos(-1.0);
const std::vector<int> dy2 = {0, 1}, dx2 = {1, 0};  // 右，下
const std::vector<int> dy4 = {0, 1, 0, -1}, dx4 = {1, 0, -1, 0};    // 右，下，左，上
const std::vector<int> dy8 = { 0, -1, 0, 1, 1, -1, -1, 1 }, dx8 = { 1, 0, -1, 0, 1, 1, -1, -1 };

using namespace std;

class Circle {
public:
    unsigned int n;
    vector<long long> circle;
    vector<long long> dp;
    long long total = 0;

public:
    Circle(vector<long long> circle) : n(circle.size()), circle(circle) {
        this->dp.resize(n * 2 + 1, 0);
        for (int i = 0; i < n * 2; ++i) {
            this->dp[i + 1] = this->dp[i] + circle[i % n];
            this->total += circle[i % n];
        }
        this->total /= 2;
    }

    long long get(int i) const {
        return circle[i % this->n];
    }

    // [i, j)の和
    long long distance(int i, int j) const {
        if (i > j) {
            j += this->n;
        }

        i %= 2 * this->n;
        j %= 2 * this->n;

        return this->dp[j] - this->dp[i];
    }
};

bool can_make(int l, int r, const int N, const LL total, const LL x, const Circle &circle) {
    assert(l <= r);

    // x以上の最小の数
    int low = r, high = N + l;
    LL ans = -1;
    while (high - low > 1) {
        int middle = (low + high) / 2;
        LL sum = circle.distance(r + 1, middle);
        if (sum >= x) {
            high = middle;
            ans = sum;
        }
        else {
            low = middle;
        }
    }

    return (ans >= x and (total - ans) >= x);
}

bool ok(const LL x, int N, const Circle &circle) {

    // しゃくとり[l, r]
    LL len = 0;
    int l = 0;
    for (int r = 0; l < N and abs(l - r) < N; ++r) {
//        cout << l << ":" << r << "(" << len << ")" << endl;
        // rの分をいれる
        len += circle.get(r);

        while (l < N and len - circle.get(l) >= x) {
            // lの分を消す
            len -= circle.get(l);
            ++l;
        }

        if (len >= x) {
            if (can_make(l, r, N, circle.total - len, x, circle)) {
                return true;
            }
        }
    }

    return false;
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    LL N;
    cin >> N;

    auto A = make_v<LL>(N);
    FOR(i, 0, N) {
        cin >> A[i];
    }
    Circle circle(A);

    long long low = -1, high = circle.total + 1;
    // (low, high)
    while (high - low > 1) {
        long long middle = (low + high) / 2;
        if (ok(middle, N, circle)) {
            low = middle;
        }
        else {
            high = middle;
        }
    }

    print(low);


    return 0;
}




Measured memory_bytes: 6748