1.0 KB | 1039 chars
"""
[22172: Веревочная почта](https://www.acmicpc.net/problem/22172)
Tier: Bronze 1
Category: greedy, implementation
"""
import sys
from math import sqrt, pi, sin, factorial, ceil, floor
from datetime import datetime, timedelta
SYS_INPUT = True
RECURSION_LIMIT = 10 ** 7
SET_RECURSION = False
BLANK = " "
if SET_RECURSION:
sys.setrecursionlimit(RECURSION_LIMIT)
inp = lambda : sys.stdin.readline().rstrip() if SYS_INPUT else input()
mii = lambda : [*map(int,inp().split())]
mfi = lambda : [*map(float,inp().split())]
ii = lambda : int(inp())
fi = lambda : float(inp())
isplit = lambda : inp().split()
p = print
def gcd(a, b): return gcd(b, a % b) if b > 0 else a
def lcm(a, b): return a * b // gcd(a, b)
def solve():
n = ii()
l = mii()
pos = 0
neg = 0
for i in range(n):
if i + 1 < l[i]:
pos = max(pos, l[i] - (i + 1))
else:
neg = max(neg, (i + 1) - l[i])
ans = min(pos * 2 + neg, neg * 2 + pos)
p(ans)
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
ret = solve()