#include <bits/stdc++.h>

using namespace std;
const int N = 500010;
int f[N][2];
int a[N];

int main() {
    freopen("5.in", "r", stdin);
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++) cin >> a[i];
    /*
    8
    1 2 8 3 3 4 4 5

    10
    8 1 1 2 3 4 5 6 7 8
    */
    // 1、处理f[i][1]
    for (int i = 1; i <= n; i++) {
        if (a[i] == a[i - 1]) f[i][1] = a[i] + 1;
        if (a[i] == f[i - 1][1]) f[i][1] = a[i] + 1;
    }

    // 2、处理f[i][0]
    for (int i = 1; i <= n; i++) f[i][0] = max({a[i], f[i - 1][0], f[i - 1][1]});

    cout << max(f[n][0], f[n][1]) << endl;

    return 0;
}