Buggy python submission (verdict: Runtime Error):
#!usr/bin/env python3
from collections import defaultdict,deque
from heapq import heappush, heappop
import sys
import math
import bisect
import random
def LI(): return [int(x) for x in sys.stdin.readline().split()]
def I(): return int(sys.stdin.readline())
def LS():return [list(x) for x in sys.stdin.readline().split()]
def S():
    res = list(sys.stdin.readline())
    if res[-1] == "\n":
        return res[:-1]
    return res

def IR(n):
    return [I() for i in range(n)]
def LIR(n):
    return [LI() for i in range(n)]
def SR(n):
    return [S() for i in range(n)]
def LSR(n):
    return [LS() for i in range(n)]

sys.setrecursionlimit(1000000)
mod = 1000000007

n = I()
a = LI()
for i in range(n):
    a[i] -= i+1
a.sort()
b = a[n>>1]
ans = 0
for i in a:
    ans += abs(i-b)
if n%2:
    b = a[(n>>1)+1]
    ans_ = 0
    for i in a:
        ans_ += abs(i-b)
    if ans > ans_:
        ans = ans_
    b = (a[(n>>1)+1]+a[n>>1])>>1
    ans_ = 0
    for i in a:
        ans_ += abs(i-b)
    if ans > ans_:
        ans = ans_
print(ans)


Fixed submission:
#!usr/bin/env python3
from collections import defaultdict
from collections import deque
from heapq import heappush, heappop
import sys
import math
import bisect
import random
def LI(): return list(map(int, sys.stdin.readline().split()))
def I(): return int(sys.stdin.readline())
def LS():return list(map(list, sys.stdin.readline().split()))
def S(): return list(sys.stdin.readline())[:-1]
def IR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = I()
    return l
def LIR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = LI()
    return l
def SR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = S()
    return l
def LSR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = SR()
    return l
mod = 1000000007

#A
def A():
    return

#B
def B():
    return

#C
def C():
    n = I()
    a = LI()
    for i in range(n):
        a[i] -= i+1
    a.sort()
    b = sum(a)//n
    ans = 0
    for i in range(n):
        ans += abs(a[i]-b)
    ans2 = 0
    b += 1
    for i in range(n):
        ans2 += abs(a[i]-b)
    ans3 = 0
    b = a[n//2]
    for i in range(n):
        ans3 += abs(a[i]-b)
    print(min(ans,ans2,ans3))

#D
def D():
    return

#E
def E():
    return

#F
def F():
    return

#G
def G():
    return

#H
def H():
    return

#Solve
if __name__ == "__main__":
    C()

Buggy python submission (verdict: Time Limit Exceeded):
#!usr/bin/env python3
from collections import defaultdict
from collections import deque
from heapq import heappush, heappop
import sys
import math
import bisect
import random
def LI(): return list(map(int, sys.stdin.readline().split()))
def I(): return int(sys.stdin.readline())
def LS():return list(map(list, sys.stdin.readline().split()))
def S(): return list(sys.stdin.readline())[:-1]
def IR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = I()
    return l
def LIR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = LI()
    return l
def SR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = S()
    return l
def LSR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = SR()
    return l
mod = 1000000007

#A
def A():
    return

#B
def B():
    return

#C
def C():
    n = I()
    a = LI()
    for i in range(n):
        a[i] -= i+1
    a.sort()
    ans = float("inf")
    for b in a:
        m = 0
        for i in range(n):
            m += abs(a[i]-b)
        ans = min(ans,m)
    print(ans)

#D
def D():
    return

#E
def E():
    return

#F
def F():
    return

#G
def G():
    return

#H
def H():
    return

#Solve
if __name__ == "__main__":
    C()


Fixed submission:
#!usr/bin/env python3
from collections import defaultdict
from collections import deque
from heapq import heappush, heappop
import sys
import math
import bisect
import random
def LI(): return list(map(int, sys.stdin.readline().split()))
def I(): return int(sys.stdin.readline())
def LS():return list(map(list, sys.stdin.readline().split()))
def S(): return list(sys.stdin.readline())[:-1]
def IR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = I()
    return l
def LIR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = LI()
    return l
def SR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = S()
    return l
def LSR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = SR()
    return l
mod = 1000000007

#A
def A():
    return

#B
def B():
    return

#C
def C():
    n = I()
    a = LI()
    for i in range(n):
        a[i] -= i+1
    a.sort()
    b = sum(a)//n
    ans = 0
    for i in range(n):
        ans += abs(a[i]-b)
    ans2 = 0
    b += 1
    for i in range(n):
        ans2 += abs(a[i]-b)
    ans3 = 0
    b = a[n//2]
    for i in range(n):
        ans3 += abs(a[i]-b)
    print(min(ans,ans2,ans3))

#D
def D():
    return

#E
def E():
    return

#F
def F():
    return

#G
def G():
    return

#H
def H():
    return

#Solve
if __name__ == "__main__":
    C()