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 C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>

using namespace std;

#define DUMP(x) std::cout << (#x) << " = " << (x) << "\n"
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define REP(i, k, n) for (int i = (k); i < (int)(n); ++ i)
#define ALL(r) r.begin(), r.end()
#define DUP(x, y) (((x) + (y) - 1) / (y))

using ll = std::int64_t;
using vint = std::vector<int>;
using vll = std::vector<ll>;
using pint = std::pair<int, int>;

constexpr std::int32_t INF = 1001001001;

void Main() {
    int n;
    cin >> n;
    vint h(n);
    rep(i, n) cin >> h[i];

    int ans = 0;
    while (true) {
        int l = -1;
        int r = -1;

        rep(i, n) {
            if (l == -1 && h[i] > 0) {
                l = i;
                continue;
            }
            if (l != -1 && h[i] <= 0) {
                r = i;
                break;
            }
        }
        if (l == -1)break;
        if (r == -1)r = n;
        REP(i, l, r) {
            --h[i];
        }
        ++ans;
    }
    cout << ans << endl;
}

int main() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << std::fixed << std::setprecision(15);
    Main();
    return 0;
}