Problem:
Score : 300 points

Problem Statement

In a flower bed, there are N flowers, numbered 1,2,......,N. Initially, the heights of all flowers are 0.
You are given a sequence h=\{h_1,h_2,h_3,......\} as input. You would like to change the height of Flower k to h_k for all k (1 \leq k \leq N), by repeating the following "watering" operation:

Specify integers l and r. Increase the height of Flower x by 1 for all x such that l \leq x \leq r.

Find the minimum number of watering operations required to satisfy the condition.

Constraints

1 \leq N \leq 100

0 \leq h_i \leq 100

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
h_1 h_2 h_3 ...... h_N

Output

Print the minimum number of watering operations required to satisfy the condition.

Sample Input 1

4
1 2 2 1

Sample Output 1

2

The minimum number of watering operations required is 2.
One way to achieve it is:

Perform the operation with (l,r)=(1,3).

Perform the operation with (l,r)=(2,4).

Sample Input 2

5
3 1 2 3 1

Sample Output 2

5

Sample Input 3

8
4 23 75 0 23 96 50 100

Sample Output 3

221

Solution in Perl (v5.18.2) (judge verdict: Accepted)

$n=<>;
@h=glob<>;
print+&f(@h);

sub f{
    my @a = @_;
    my $i=0;
    my $div=0;
    my @l;
    my @r;
    shift(@a) while($a[0]==0&&$#a>0);
    pop(@a) while($a[$#a]==0&&$#a>0);
    return $a[0] if ($#a==0);
    foreach(@a){
        if ($_==0){
            @l=@a[0..$i-1];
            @r=@a[$i+1..$#a];
            $div=1;
            last;
        }
        $i++;
    }
    if ($div==0){
        $_-- for(@a);
        return 1+&f(@a);
    }else{
        return &f(@l)+&f(@r);
    }
}