[백준] 2847번 : 게임을 만든 동준이 - Python(파이썬)

https://www.acmicpc.net/problem/2847

n=int(input())
arr=[0]*n
count=0
for i in range(n):
    arr[i]=int(input())
for i in range(n-1,0,-1):
    if arr[i]<=arr[i-1]:
        count+=arr[i-1]-arr[i]+1
        arr[i-1]=arr[i]-1
print(count)