import java.util.*;
import java.io.*;

public class TwoFourEight {
    static int[] list;
    static int max;
    static int[][] dp;
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new FileReader("248.in"));
        PrintWriter pw = new PrintWriter(new FileWriter("248.out"));
        StringTokenizer st = new StringTokenizer(br.readLine());

        int n = Integer.parseInt(st.nextToken());
        list = new int[n];
        max = Integer.MIN_VALUE;
        dp = new int[n+1][n];
        for (int i = 0; i < n; i++) {
            st = new StringTokenizer(br.readLine());
            list[i] = Integer.parseInt(st.nextToken());
            max = Math.max(list[i], max);
        }

        pw.println(maxNum(n,n-1));
        pw.close();
    }

    public static int maxNum(int n, int i){
        if(dp[n][i] > 0)
            return dp[n][i];
        if(n == 1)
            return dp[n][i] = list[0];
        if(i == 0)
            return dp[n][i] = max;
        if(list[i] == list[i-1]) {
            list[i-1]++;
            for(int x = i; x<n-1; x++)
                list[x] = list[x+1];
            //System.out.println(Arrays.toString(list));
            max = Math.max(max, list[i-1]);
            return dp[n][i] = Math.max(max, maxNum(n - 1, n - 2));
        }
        max = Math.max(max, list[i]);
        return dp[n][i] = Math.max(max, maxNum(n, i-1));
    }
}