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 Python (3.4.3) (judge verdict: Accepted)

#!/usr/bin/env python3
import sys
from math import *
from itertools import *
from collections import *
from functools import *
try:
    from math import gcd
except Exception:
    from fractions import gcd


def solve(N: int, h: "List[int]"):
    ret = 0
    while True:
        b = 0
        while b < len(h) and  h[b] == 0:
            b += 1

        e = b
        while e < len(h) and 0 < h[e]:
            e += 1

        if b == e:
            break

        ret += 1
        for i in range(b, e):
            h[i] -= 1

    return ret


def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    h = [ int(next(tokens)) for _ in range(N) ]  # type: "List[int]"
    result = solve(N, h)
    print(result)

if __name__ == '__main__':
    main()