# Python3 program to find min elements to

# change so array is strictly increasing

# Find min elements to remove from array

# to make it strictly increasing

def minRemove(arr, n):

    LIS = [0 for i in range(n)]

    len = 0

    # Mark all elements of LIS as 1

    for i in range(n):

        LIS[i] = 1

    # Find LIS of array

    for i in range(1, n):

        for j in range(i):

            if (arr[i] > arr[j] and (i-j)<=(arr[i]-arr[j]) ):

                LIS[i] = max(LIS[i], LIS[j] + 1)

        len = max(len, LIS[i])

    # Return min changes for array

    # to strictly increasing

    return (n - len)

# Driver Code

arr = [ 1, 2, 6, 5, 4 ]

n = len(arr)

print(minRemove(arr, n))

# This code is contributed by Azkia Anam.