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 (GCC 5.4.1) (judge verdict: Accepted)

#include<stdio.h>

int ans=0;

void count(int*,int,int);
void pluser(int*,int,int);

void pluser(int array[],int left,int right){
  int pivot=array[left];
  int i;
  for(i=left;i<=right;i++){
    if(array[i]<pivot)pivot=array[i];
  }
  for(i=left;i<=right;i++){
    array[i]-=pivot;
  }
  ans+=pivot;
  count(array,left,right);
}

void count(int array[],int left,int right){
  int i,j,c;
  j=1;
  c=0;
  for(i=left;i<=right;i++){
    if(array[i]==0)c++;
  }
  int zero[c+2];
  zero[0]=left-1;
  zero[c+1]=right+1;
  for(i=left;i<=right;i++){
    if(array[i]==0){
      zero[j]=i;
      j++;
    }
  }

  if(c==0){
    pluser(array,left,right);
  }
  for(i=0;i<c+1;i++){
    if(zero[i]+1==zero[i+1]){
      continue;
    }else if(zero[i]+2==zero[i+1]){
      ans+=array[zero[i]+1];
      array[zero[i]+1]=0;
    }else{
      pluser(array,zero[i]+1,zero[i+1]-1);
    }
  }

}

int main(void){
  int n,i,j,ze;
  j=1;
  while(scanf("%d",&n)!=1);
  int array[n];
  for(i=0;i<n;i++){
    while(scanf("%d",&array[i])!=1);
  }
  count(array,0,n-1);
  printf("%d\n",ans);

  return 0;
}