import java.util.Arrays;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);

        int ans = 0;
        int N = in.nextInt();
        int[] values = new int[N];

        for (int i = 0; i < N; i++) {
            values[i] = in.nextInt();
        }
        // 先頭と末尾を0で埋める
        int[] valuesWithPadding = new int[N+2];
        for (int i = 0; i < N; i++) {
            valuesWithPadding[i+1] = values[i];
        }

        while (true) {
            
            // 0でない数字の塊の数を数える
            int count = 0;
            for (int i = 1; i < N+2; i++) {
                if (valuesWithPadding[i] != 0) {
                    if (valuesWithPadding[i - 1] == 0) {
                        count++;
                    }
                }
            }
            if (count == 0) break;
            for (int i = 0; i < N+2; i++) {
                if (valuesWithPadding[i] != 0) {
                    valuesWithPadding[i] -= 1;
                }
            }
            ans += count;
        }
        System.out.println(ans);

    }

}

/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz