Problem:
 Score : 600 points    Problem Statement Snuke got an integer sequence of length N from his mother, as a birthday present. The i -th (1 ≦ i ≦ N) element of the sequence is a_i . The elements are pairwise distinct.
He is sorting this sequence in increasing order.
With supernatural power, he can perform the following two operations on the sequence in any order:   Operation 1 : choose 2 consecutive elements, then reverse the order of those elements.  Operation 2 : choose 3 consecutive elements, then reverse the order of those elements.   Snuke likes Operation 2 , but not Operation 1 . Find the minimum number of Operation 1 that he has to perform in order to sort the sequence in increasing order.      Constraints  1 ≦ N ≦ 10^5  0 ≦ A_i ≦ 10^9  If i ≠ j , then A_i ≠ A_j .  All input values are integers.         Input The input is given from Standard Input in the following format:  N  A_1 : A_N       Output Print the minimum number of times Operation 1 that Snuke has to perform.        Sample Input 1 4
2
4
3
1      Sample Output 1 1  The given sequence can be sorted as follows:   First, reverse the order of the last three elements. The sequence is now: 2,1,3,4 .  Then, reverse the order of the first two elements. The sequence is now: 1,2,3,4 .   In this sequence of operations, Operation 1 is performed once. It is not possible to sort the sequence with less number of Operation 1 , thus the answer is 1 .       Sample Input 2 5
10
8
5
3
2      Sample Output 2 0

Solution (Python):
import sys
def input(): return sys.stdin.readline().strip()
n=int(input())
a=[int(input()) for i in range(n)]
b=sorted(a)
a0=[]
b0=[]
for i in range(n):
    if i%2==0:
        a0.append(a[i])
        b0.append(b[i])
print(len(a0)-len(list(set(a0) & set(b0))))

Solution (Python):
N = int(input())
A = [(int(input()),i) for i in range(N)]

A = sorted(A,key = lambda x:x[0])

diff = 0
for i in range(len(A)):
  if A[i][1] % 2 != i % 2:
    diff += 1
    
print(diff // 2)

Solution (Python):
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
sys.setrecursionlimit(10 ** 7)

from bisect import bisect_left

n, *a = map(int, read().split())
b = sorted(a)
cnt = 0
for i, aa in enumerate(a):
    if abs(i - bisect_left(b, aa)) % 2 == 1:
        cnt += 1
print(cnt // 2)

Solution (Python):
n = int(input())
kl = []
for i in range(n):
    a = int(input())
    kl.append(a)
from collections import defaultdict
dic = defaultdict(int)

for idx, i in enumerate(sorted(kl)):
    dic[i] = idx + 1
cl = [k for k in kl]

al = []
bl = []
for i, c in enumerate(cl):
    if i % 2 == 0:
        al.append(c)
    else:
        bl.append(c)


ans = 0
for b in bl:
    if dic[b] % 2 != 0:
        ans += 1

print(ans)

Solution (Python):
import bisect

n = int(input())
a = [int(input()) for _ in range(n)]
b = list(a)
b.sort()
s, t = 0, 0
for i in range(n):
    x = bisect.bisect_left(b, a[i])
    if i % 2 == 0 and x % 2 == 1:
        s += 1
    elif i % 2 == 1 and x % 2 == 0:
        t += 1
print(max(s, t))

Solution (Python):
import sys

input = sys.stdin.readline
sys.setrecursionlimit(100000)

mod = 998244353


def read_values():
    return map(int, input().split())


def read_index():
    return map(lambda x: int(x) - 1, input().split())


def read_list():
    return list(read_values())


def read_lists(N):
    return [read_list() for n in range(N)]


class V:
    def __init__(self, f, v=None):
        self.f = f
        self.v = v

    def __str__(self):
        return str(self.v)

    def ud(self, n):
        if n is None:
            return

        if self.v is None:
            self.v = n
            return
        self.v = self.f(self.v, n)


def main():
    N = int(input())
    A = [(int(input()), n % 2) for n in range(N)]
    A.sort()

    res = 0
    for i, (_, j) in enumerate(A):
        if i % 2 != j:
            res += 1

    print(res // 2)


if __name__ == "__main__":
    main()

Solution (Python):
import copy

N=int(input())
A=[]
for i in range(N):
    A.append(int(input()))

a=copy.copy(A)
A.sort()
dic={}
for i in range(0,N):
    dic[a[i]]=0
    dic[a[i]]=i

ans=0
for i in range(0,N):
    if i%2==1:
        if dic[A[i]]%2==0:
            ans+=1

print(ans)

Solution (Python):
n = int(input())
a = [int(input()) for _ in range(n)]
b = {}
for i, j in enumerate(sorted(a)):
    b[j] = i
ans = 0
for i, j in enumerate(a):
    ans += (b[j] - i) % 2
print(ans // 2)

Solution (Python):
N = int(input())
A = [int(input()) * N + i for i in range(N)]
A.sort()
cnt = 0
for i in range(N):
  d = (A[i] % N) % 2
  if d % 2 != i % 2:
    cnt += 1
print(cnt//2)

Solution (Python):
N=int(input())
A=[]
for i in range(N):
    A.append(int(input()))
d={}
B=sorted(A)
for i in range(N):
    d[B[i]]=i
cnt=0
for i in range(N):
    if abs(i-d[A[i]])%2==1:
        cnt+=1
print(cnt//2)

Solution (Python):
from collections import defaultdict
N = int(input())
A = [(int(input()), i) for i in range(1, N+1)]
A.sort()
c = 0
for i, (a, j) in enumerate(A, 1):
    c += (i-j)&1
print(c//2)

Solution (Python):

from collections import defaultdict,deque
from heapq import heappush, heappop
from bisect import bisect_left, bisect_right
import sys, random, itertools, math
sys.setrecursionlimit(10**5)
input = sys.stdin.readline
sqrt = math.sqrt
def LI(): return list(map(int, input().split()))
def LF(): return list(map(float, input().split()))
def LI_(): return list(map(lambda x: int(x)-1, input().split()))
def II(): return int(input())
def IF(): return float(input())
def S(): return input().rstrip()
def LS(): return S().split()
def IR(n): return [II() for _ in range(n)]
def LIR(n): return [LI() for _ in range(n)]
def FR(n): return [IF() for _ in range(n)]
def LFR(n): return [LI() for _ in range(n)]
def LIR_(n): return [LI_() for _ in range(n)]
def SR(n): return [S() for _ in range(n)]
def LSR(n): return [LS() for _ in range(n)]
mod = 1000000007
inf = 1e10


def solve():
    n = II()
    a = IR(n)
    d = defaultdict(int)
    b = a[::1]
    b.sort()
    for i, bi in enumerate(b):
        d[bi] = i
    ans = [0, 0]
    for i in range(n):
        ans[i & 1] += d[a[i]] & 1 != i & 1
    print(max(ans))
    return



if __name__ == '__main__':
    solve()

Solution (Python):

from bisect import bisect_left, bisect_right
n = int(input())
a = [int(input()) for _ in range(n)]
b = sorted(a)

ans = 0
for i in range(n):
    if (i - bisect_left(b, a[i])) % 2 == 1:
        ans += 1
print(ans // 2)

Solution (Python):
def coord_compress(A):
    B = {a: i for i, a in enumerate(sorted(set(A)), 1)}
    return [B[a] for a in A]

N = int(input())
A = [int(input()) for _ in range(N)]
A = coord_compress(A)
A_odd, A_even = A[::2], A[1::2]
ans = 0
for a in A_odd:
    if a % 2 == 0: ans += 1
print(ans)

Solution (Python):
N = int(input())
As = [(int(input()),i) for i in range(N)]
As.sort()
cnt = 0
for i,(n, j) in enumerate(As):
    if j%2 != i%2:
        cnt += 1
    
print(cnt//2)

Solution (Python):
def examA():
    S = SI()
    if "W" in S and not "E" in S:
        print("No")
    elif "E" in S and not "W" in S:
        print("No")
    elif "N" in S and not "S" in S:
        print("No")
    elif "S" in S and not "N" in S:
        print("No")
    else:
        print("Yes")
    return

def examB():
    N = I()
    A = [I()for _ in range(N)]
    ans = 0
    for i in range(N-1):
        ans += A[i]//2
        if A[i]%2 and A[i+1]>=1:
            ans += 1
            A[i+1] -= 1
    ans += A[N-1]//2
    print(ans)
    return

def examC():
    N = I()
    A = [I()for _ in range(N)]
    if N==1:
        print(0)
        return
    odd = set()
    for i in range(N):
        if i&1==0:
            odd.add(A[i])
    A.sort()
    ans = 0
    for i in range((N+1)//2):
        if A[i*2] in odd:
            continue
        ans += 1
    print(ans)
    return

def examD():
    N = I()
    S = [I()for _ in range(N)]

    ans = 0
    print(ans)
    return

def examE():
    ans = 0
    print(ans)
    return

def examF():
    ans = 0
    print(ans)
    return

import sys,bisect,itertools,heapq,math,random
from copy import deepcopy
from heapq import heappop,heappush,heapify
from collections import Counter,defaultdict,deque
def I(): return int(sys.stdin.readline())
def LI(): return list(map(int,sys.stdin.readline().split()))
def LSI(): return list(map(str,sys.stdin.readline().split()))
def LS(): return sys.stdin.readline().split()
def SI(): return sys.stdin.readline().strip()
global mod,mod2,inf,alphabet,_ep
mod = 10**9 + 7
mod2 = 998244353
inf = 10**18
_ep = 10**(-12)
alphabet = [chr(ord('a') + i) for i in range(26)]

sys.setrecursionlimit(10**6)

if __name__ == '__main__':
    examC()

"""

"""

Solution (Python):
N, *A = map(int, open(0))
print(len(set(A[1::2]) & set(sorted(A)[::2])))

Solution (Python):
import sys
from operator import itemgetter

read = sys.stdin.read
readline = sys.stdin.readline

N, *A = map(int, read().split())
z, _ = zip(*sorted(enumerate(A), key=itemgetter(1)))
z, _ = zip(*sorted(enumerate(z), key=itemgetter(1)))
cnt = 0
for i in range(N):
    if i % 2 != z[i] % 2:
        cnt += 1
print(cnt // 2)

Solution (Python):

n = int(input())
a = []
for i in range(n):
    a.append(int(input()))
b = a[::]
b.sort()

dic = dict()
for i,v in enumerate(b):
    dic[v]=i

num = 0    
for i,v in enumerate(a):
    ind = dic[v]
    num += ((i-ind)%2)
print(num//2)

Solution (Python):
N, *A = map(int, open(0).read().split())
B = sorted(A)
dic = {B[i]:i for i in range(N)}
ans = sum((i+1)%2==dic[n]%2 for i,n in enumerate(A))
print(ans//2)

Solution (Python):
N, *A = map(int, open(0).read().split())
ans = 0
B = sorted(A)
dic = {B[i]:i for i in range(N)}
for i,n in enumerate(A):
  if i%2!=dic[n]%2:
    ans += 1
print(ans//2)

Solution (Python):
N = int(input())
A = [int(input()) for _ in range(N)]

D = {a:i for i,a in enumerate(sorted(A))}

A = [D[A[i]] for i in range(N)]

count = 0

for i in range(N):
    if i%2 == 0 and A[i]%2 != 0:
        count += 1

print(count)

Solution (Python):
N = int(input())
A = [int(input()) for _ in range(N)]

D = {a:i for i,a in enumerate(sorted(A))}

A = [D[A[i]] for i in range(N)]

odd = [A[i] for i in range(N) if i%2 == 0]
even = [A[i] for i in range(N) if i%2 == 1]

odd.sort()
even.sort()

B = []

for i in range(N):
    if i%2 == 0:
        B.append(odd[i//2])
    else:
        B.append(even[i//2])

count = 0

for i in range(N):
    if i%2 == 0 and B[i]%2 != 0:
        count += 1

print(count)

Solution (Python):
n = int(input())
a = []
for _ in range(n):
    a.append(int(input()))
import numpy as np
lis = np.argsort(np.array(a))

ans=0
for i in range(n):
    if i%2 != lis[i]%2:
        ans+=1
print(ans//2)

Solution (Python):
N=int(input())
A=[int(input()) for i in range(N)]
odd =[A[i] for i in range(N) if i%2 ==0]
even=[A[i] for i in range(N) if i%2 ==1]
import collections
table=collections.defaultdict(int)
table2=collections.defaultdict(int)
A.sort()
for i in range(N):
  if i %2==0:
    table[A[i]]+=1
for x in odd:
  table2[x]+=1
ans=0

for x in table:
  ans+=(table[x] -table2[x])

print(ans)

Solution (Python):
n = int(input())
b = [ [] for _ in range(n) ]
for i in range(n):
    a = int(input())
    b[i] = [a, i]

b.sort()
cnt = 0
for i in range(n):
    if (i & 1) != (b[i][1] & 1):
        cnt += 1

print(cnt // 2)

Solution (Python):
import sys
input = sys.stdin.buffer.readline
import bisect

def main():
    N =  int(input())
    
    odd,al = [],[]
    for i in range(N):
        a = int(input())
        if i%2 == 0:
            odd.append(a)
        al.append(a)
            
    odd.sort()
    al.sort()
    ans = 0
    for i in range(-(-N//2)):
        num = odd[i]
        index = bisect.bisect_left(al,num)
        if index%2 == 1:
            ans += 1
            
    print(ans)

if __name__ == "__main__":
    main()

Solution (Python):
def main():
    N, *A = map(int, open(0).read().split())
    B = sorted(A)
    S = [set(),set()]
    for i in range(N):
        S[i&1].add(B[i])
    print(sum(a not in S[i&1] for i, a in enumerate(A))//2)


if __name__ == "__main__":
    main()

Solution (Python):
N = int(input())
A = [int(input()) for _ in range(N)]

mp = {}
for i, j in enumerate(A):
	mp[j] = i % 2
	
A.sort()

ans = 0
for i, j in enumerate(A):
	if i % 2 != mp[j]: ans += 1

print(ans // 2)

Solution (Python):
from sys import stdout
printn = lambda x: stdout.write(str(x))
inn = lambda : int(input())
inl   = lambda: list(map(int, input().split()))
inm   = lambda:      map(int, input().split())
ins = lambda : input().strip()
DBG = True 
BIG = 999999999
R = 10**9 + 7

def ddprint(x):
  if DBG:
    print(x)

n = inn()
a = []
for i in range(n):
    a.append((inn(),i))
a.sort()
cnt = 0
for i in range(0,n,2):
    cnt += a[i][1]%2
print(cnt)

Solution (Python):
import copy
from collections import defaultdict
n=int(input())
a=[int(input()) for _ in range(n)]
b=copy.copy(a)
b.sort()
d=defaultdict(int)
for i in range(n):
  d[b[i]]=i
ans=0
for i in range(n):
  if (d[a[i]]-i)%2==1:
    ans+=1
print(ans//2)

Solution (Python):
import sys
input = sys.stdin.readline
read = sys.stdin.read

n = int(input())
A = map(int, read().split())
L = sorted([(j, i) for i, j in enumerate(A)])
count = 0
for i in range(n):
  count += (L[i][1]-i)%2
print(count//2)

Solution (Python):
import sys
input = sys.stdin.readline
read = sys.stdin.read

n = int(input())
A = map(int, read().split())
L = sorted([(j, i) for i, j in enumerate(A)])
count = 0
for i in range(n):
  count += (L[i][1]-i)%2
ans = (count+1) // 2
print(ans)

Solution (Python):
import sys
input = sys.stdin.readline
read = sys.stdin.read

n = int(input())
A = map(int, read().split())
L = sorted([(j, i) for i, j in enumerate(A)])
count = 0
for i in range(n):
  if (L[i][1]-i)%2:
    count += 1
ans = (count+1) // 2
print(ans)

Solution (Python):
N = int(input())
A = [int(input()) for _ in range(N)]

import bisect

B = sorted(A)
ans = 0
for i in range(N):
    idx = bisect.bisect_left(B, A[i])
    if (i-idx)%2 == 1:
        ans += 1

print(ans//2)

Solution (Python):
import sys, bisect, math, itertools, string, queue, copy


from collections import Counter,defaultdict,deque
from itertools import permutations, combinations
from heapq import heappop, heappush

sys.setrecursionlimit(10**8)
mod = 10**9+7
def inp(): return int(input())
def inpm(): return map(int,input().split())
def inpl(): return list(map(int, input().split()))
def inpls(): return list(input().split())
def inplm(n): return list(int(input()) for _ in range(n))
def inplL(n): return [list(input()) for _ in range(n)]
def inplT(n): return [tuple(input()) for _ in range(n)]
def inpll(n): return [list(map(int, input().split())) for _ in range(n)]
def inplls(n): return sorted([list(map(int, input().split())) for _ in range(n)])
 
def main():
    n = inp()
    a = []
    for i in range(n):
        a.append((int(input()),i))
    a.sort()
    ans = 0
    for i in range(0,n,2):
        if a[i][1]%2 == 1:
            ans += 1
    print(ans)
    
if __name__ == "__main__":
    main()

Solution (Python):
from bisect import *
from collections import *
from fractions import gcd
from math import factorial
from itertools import *
N=int(input())
A=[int(input()) for i in range(N)]
sortA=sorted(A)
A0=[]
A1=[]
sortA0=[]
sortA1=[]
for i in range(N):
    if i%2==0:
        A0.append(A[i])
        sortA0.append(sortA[i])
    else:
        A1.append(A[i])
        sortA1.append(sortA[i])

A0=Counter(A0)
A1=Counter(A1)
sortA0=Counter(sortA0)
sortA1=Counter(sortA1)

count0=0
for a in A0:
    if a in sortA0:
        count0+=round(abs(sortA0[a]-A0[a]))
    else:
        count0+=A0[a]
print(count0)

Solution (Python):
import numpy as np
N = int(input())
a = np.array([int(input()) for _ in range(N)])
even_a = a[1::2]
b = np.sort(a)
even_b = b[1::2]
print(len(even_a) - len(set(even_a) & set(even_b)))

Solution (Python):
N = int(input())
A = [int(input()) for _ in range(N)]
B = sorted(A)

oddA = set(A[::2])
oddB = set(B[::2])

ans = len(oddA) - len(oddA & oddB)
print(ans)

Solution (Python):

import sys


def val_arg_tpls_sort(lis):
    val_arg_tpls = (
        (val, i) for i, val in enumerate(lis)
    )
    return list(sorted(val_arg_tpls))


def count_odd_in_even(val_arg_tpls):
    cnt = 0
    for _, arg in val_arg_tpls[::2]:
        cnt += arg % 2
    return cnt


def solve(N: int, A: "List[int]"):
    sorted_tpls = val_arg_tpls_sort(A)
    cnt = count_odd_in_even(sorted_tpls)
    print(cnt)
    return



def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  
    A = [int(next(tokens)) for _ in range(N)]  
    solve(N, A)

if __name__ == '__main__':
    main()

Solution (Python):

N=int(input())
A=[]
for i in range(N):
    A.append([int(input()),i])

As=sorted(A)

cnt=0
for i in range(N):
    if (As[i][1]-i)%2==1:
        cnt+=1

print(cnt//2)

Solution (Python):
import sys
input = sys.stdin.readline

N = int(input())
A = [(int(input()), i) for i in range(N)]
A_sorted = sorted(A)
count = 0
for i in range(N):
    count += (A_sorted[i][1] - i) % 2
print(count // 2)

Solution (Python):

import sys
INF = float("inf")


def solve(N: int, A: "List[int]"):

    
    dic = {}
    for i, a in enumerate(sorted(A)):
        dic[a] = i
    B = [dic[a] for a in A]

    
    count = 0
    for i in range(0, N, 2):
        if B[i] % 2 == 1:
            count += 1
    print(count)

    return


def main():

    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  
    A = [int(next(tokens)) for _ in range(N)]  
    solve(N, A)


if __name__ == '__main__':
    main()

Solution (Python):
N = int(input())
A = sorted(list({int(input()):i for i in range(N)}.items()),key=lambda x:x[0])
cnt = 0
for i in range(N):
    j = A[i][1]
    if i%2!=j%2:
        cnt += 1
print(cnt//2)

Solution (Python):
N = int(input())
A = [int(input()) for _ in range(N)]
B = sorted(A)
D = {b: i for i, b in enumerate(B)}

ans = 0
for i, a in enumerate(A):
    if (i ^ D[a]) % 2:
        ans += 1
print(ans // 2)

Solution (Python):
n=int(input())
a = [(i,int(input())) for i in range(n)]
a.sort(key=lambda x:x[1])
cnt = 0
for i,tup in enumerate(a):
  x=tup[0]
  if (x-i)%2:
    cnt += 1
print(cnt//2)

Solution (Python):
n = int(input())
A = [int(input()) for i in range(n)]
B = A[:]

D = {}
A.sort()
for i in range(n):
    D[A[i]] = i

for i in range(n):
    B[i] = D[B[i]]


ans = 0
for i in range(n):
    if i % 2 != B[i] % 2:
        ans += 1
print((ans+1) // 2)

Solution (Python):
from collections import defaultdict

N = int(input())
A = [int(input()) for _ in range(N)]
B = A[:]
B.sort()
idx = defaultdict(int)

for i in range(N):
    idx[B[i]] = i

ans = 0

for i in range(0, N, 2):
    if idx[A[i]]%2==1:
        ans += 1

print(ans)

Solution (Python):
n = int(input())
a = [int(input()) for i in range(n)]
b = sorted(a[::2])
a.sort()
now = 0
ans = 0
br = len(b)
for k,v in enumerate(a):
  if b[now] == v:
    if k % 2:
      ans += 1
    now += 1
  if now == br:
    break
print(ans)

Solution (Python):
n=int(input())
A=[[0]*2 for i in range(n)]
for i in range(n):
  A[i][0]=int(input())
  A[i][1]=i%2
A.sort(key=lambda x:x[0])
ans=0
for i in range(n):
  if i%2==0:
    ans=ans+A[i][1]
print(ans)

Solution (Python):
import sys
input = sys.stdin.readline

N = int(input())

A = []
A_append = A.append
for i in range(1, N + 1):
    a = int(input())
    A_append([a, i])

A.sort(key = lambda x: x[0])

count = 0
for i in range(N):
    if A[i][1] % 2 == (i + 1) % 2:
        pass
    else:
        count += 1

print (count // 2)

Solution (Python):
import sys


stdin = sys.stdin

ri = lambda: int(rs())
rl = lambda: list(map(int, stdin.readline().split())) 
rs = lambda: stdin.readline().rstrip()  

N = ri()
A = [ri() for _ in range(N)]
x_to_i = {x:i for i, x in enumerate(sorted(A))}
rank = [x_to_i[x] for x in A]
answer = sum((i^x)&1 for i,x in enumerate(rank)) // 2
print(answer)

Solution (Python):
import sys


stdin = sys.stdin

ri = lambda: int(rs())
rl = lambda: list(map(int, stdin.readline().split())) 
rs = lambda: stdin.readline().rstrip()  

N = ri()
A = [ri() for _ in range(N)]
x_to_i = {x:i for i, x in enumerate(sorted(A))}
rank = [x_to_i[x] for x in A]
answer = sum(i&1 and (i^x)&1 for i,x in enumerate(rank))
print(answer)

Solution (Python):
import sys


stdin = sys.stdin

ri = lambda: int(rs())
rl = lambda: list(map(int, stdin.readline().split())) 
rs = lambda: stdin.readline().rstrip()  

N = ri()
A = [ri() for _ in range(N)]
B = sorted(A)
B = set(B[1::2])
C = [i%2==1 and a not in B for i, a in enumerate(A)]
print(sum(C))

Solution (Python):
import sys
import numpy as np

stdin = sys.stdin

ri = lambda: int(rs())
rl = lambda: list(map(int, stdin.readline().split())) 
rs = lambda: stdin.readline().rstrip()  

N = ri()
A = [ri() for _ in range(N)]
B = sorted(A)
B = set(B[1::2])
C = [i%2==1 and a not in B for i, a in enumerate(A)]
print(sum(C))

Solution (Python):
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

"""
・偶数番号、奇数番号の中では入れ替え放題
・偶、奇の間：並べてからスワップ。操作2を1回で、正しいものを2つ増やせる
"""

N,*A = map(int,read().split())

x_to_i = {x:i for i,x in enumerate(sorted(A))}
rank = [x_to_i[x] for x in A]

answer = sum((x^i) & 1 for i,x in enumerate(rank)) // 2
print(answer)

Solution (Python):
n = int(input())
a = [int(input()) for i in range(n)]
b = sorted(a[::2])
a.sort()
now = 0
ans = 0
br = len(b)
for k,v in enumerate(a):
  if b[now] == v:
    if k % 2:
      ans += 1
    now += 1
  if now == br:
    break
print(ans)

Solution (Python):
import bisect

N = int(input())
A = list(int(input())for i in range(N))
ans = 0
B = sorted(A)
for i in range(N):
    if i%2 != bisect.bisect_left(B, A[i])%2:
        ans += 1
print(ans//2)

Solution (Python):
import sys
import math
from collections import defaultdict

sys.setrecursionlimit(10**7)
def input():
    return sys.stdin.readline()[:-1]

mod = 10**9 + 7

def I(): return int(input())
def II(): return map(int, input().split())
def III(): return list(map(int, input().split()))
def Line(N,num):
    if N<=0:
        return [[]]*num
    elif num==1:
        return [I() for _ in range(N)]
    else:
        read_all = [tuple(II()) for _ in range(N)]
        return map(list, zip(*read_all))





from operator import itemgetter
def index_sort(A):
    return sorted(enumerate(A),key=itemgetter(1))

N = I()
A = Line(N,1)

B = index_sort(A)
num = 0
for i in range(N):
    if abs(B[i][0]-i)%2==1:
        num += 1

print(num//2)

Solution (Python):
import sys
sys.setrecursionlimit(2147483647)
INF=float("inf")
MOD=10**9+7
input=lambda:sys.stdin.readline().rstrip()
def resolve():
    n=int(input())
    A=[(int(input()),i) for i in range(n)]
    A.sort()
    d=0
    for i,tup in enumerate(A):
        a,j=tup
        d+=abs(j-i)%2

    print(d//2)
resolve()

Solution (Python):
n=int(input())
a=sorted([[int(input()),i]for i in range(n)])
print(sum([(a[i][1]-i)%2 for i in range(n)])//2)

Solution (Python):
def examC():
    N = I(); A = [I() for _ in range(N)]
    AS = sorted(A)
    A0 = A[::2]
    d = defaultdict(bool)
    for i in AS[::2]:
        d[i] = True
    ans = 0
    for i in A0:
        if not d[i]:
            ans +=1
    print(ans)

import sys,copy,bisect,itertools,heapq,math
from heapq import heappop,heappush,heapify
from collections import Counter,defaultdict,deque
def I(): return int(sys.stdin.readline())
def LI(): return list(map(int,sys.stdin.readline().split()))
def LSI(): return list(map(str,sys.stdin.readline().split()))
def LS(): return sys.stdin.readline().split()
def SI(): return sys.stdin.readline().strip()
mod = 10**9 + 7
inf = float('inf')

if __name__ == '__main__':
    examC()

Solution (Python):
from collections import namedtuple
from operator import attrgetter

Number = namedtuple('Number', 'number idx')

n = int(input())

a = []
for idx in range(n):
    k = int(input())
    a.append(Number(number=k, idx=idx))

a.sort(key=attrgetter('number'))

ret = 0
for j, a_ in enumerate(a):
    if (j - a_.idx) % 2 != 0:
        ret += 1
print(ret // 2)

Solution (Python):
N = int(input())

A = []

for i in range(N):

    a = int(input())
    A.append([a,i % 2])

A.sort()
ans = 0

for i in range(N):

    if i % 2 != A[i][1]:
        ans += 1

print (ans // 2)

Solution (Python):
print(sum([abs(k-j)%2 for k,[i,j] in enumerate(sorted([[int(input()),i] for i in range(int(input()))]))])//2)

Solution (Python):
def main():
    n=int(input())
    a=[int(input()) for _ in [0]*n]
    a=sorted([[a[i],i] for i in range(n)])
    for i in range(n):
        a[i][0]=abs(i-a[i][1])%2
    a=[i[0] for i in a]
    print(sum(a)//2)
main()

Solution (Python):

import sys
input = sys.stdin.buffer.readline


def getlist():
	return list(map(int, input().split()))


def main():
	N = int(input())
	A = []
	for i in range(N):
		a = int(input())
		A.append([a, i])
	B = sorted(A)
	ans = 0
	for i in range(N):
		if A[i][1] % 2 == 1 and B[i][1] % 2 == 0:
			ans += 1
	print(ans)

if __name__ == '__main__':
	main()

Solution (Python):
import bisect
import heapq
import itertools
import math
import operator
import os
import re
import string
import sys
from collections import Counter, deque, defaultdict
from copy import deepcopy
from decimal import Decimal
from fractions import gcd
from functools import lru_cache, reduce
from operator import itemgetter, mul, add, xor

import numpy as np

if os.getenv("LOCAL"):
    sys.stdin = open("_in.txt", "r")

sys.setrecursionlimit(10 ** 9)
INF = float("inf")
IINF = 10 ** 18
MOD = 10 ** 9 + 7



N = int(sys.stdin.readline())
A = [int(sys.stdin.readline()) for _ in range(N)]

A = np.array(A, dtype=int)

a = set(A[::2])
b = set(np.msort(A)[::2])

ans = len(a - b)
print(ans)

Solution (Python):

import bisect
import heapq
import math
import random
import sys
from collections import Counter, defaultdict, deque
from decimal import ROUND_CEILING, ROUND_HALF_UP, Decimal
from functools import lru_cache, reduce
from itertools import combinations, combinations_with_replacement, product, permutations
from operator import add, mul, sub

sys.setrecursionlimit(100000)
input = sys.stdin.readline
INF = 2**62-1


def read_int():
    return int(input())


def read_int_n():
    return list(map(int, input().split()))


def read_float():
    return float(input())


def read_float_n():
    return list(map(float, input().split()))


def read_str():
    return input().strip()


def read_str_n():
    return list(map(str, input().split()))


def error_print(*args):
    print(*args, file=sys.stderr)


def mt(f):
    import time

    def wrap(*args, **kwargs):
        s = time.time()
        ret = f(*args, **kwargs)
        e = time.time()

        error_print(e - s, 'sec')
        return ret

    return wrap


@mt
def slv(N, A):
    A_ = [(a, i%2) for i, a in enumerate(A)]
    A_.sort()

    ans = 0
    for i, (_, j) in enumerate(A_):
        if i % 2 != j:
            ans += 1
    return ans // 2


def main():
    N = read_int()
    A = [read_int() for _ in range(N)]
    print(slv(N, A))


if __name__ == '__main__':
    main()

Solution (Python):
from bisect import bisect_left

N = int(input())
A = [int(input()) for _ in range(N)]

B = sorted(A)

ret = 0
for i in range(N) :
    j = bisect_left(B, A[i])
    if i % 2 != j % 2 :
        ret += 1
        
print(ret // 2)

Solution (Python):
N=int(input())
A=[int(input()) for i in range(N)]
S=sorted(A)
from bisect import bisect_left
p=[0]*N
for i,a in enumerate(A):
    p[bisect_left(S,a)]=i
print(sum([(p[i]-i)%2 for i in range(N)])//2)

Solution (Python):
import sys
input = sys.stdin.buffer.readline
N = int(input())
a = []
d = dict()
res = 0
for i in range(N):
  a.append(int(input()))
  d[a[i]] = i
b = sorted(a)
for i in range(N):
  j = d[b[i]]
  res += abs(i - j) % 2
print(res // 2)

Solution (Python):
import sys
input = sys.stdin.readline

N = int(input())
A = [int(input()) for _ in range(N)]

B0 = set()
for i in range(N):
    if i % 2 == 0:
        B0.add(A[i])

A.sort()

ans = 0
for i in range(N):
    if i%2 == 0:
        if not A[i] in B0:
            ans += 1

print(ans)

Solution (Python):
n = int(input())
a = [int(input()) for _ in range(n)]
d = [{x: 0 for x in a} for _ in range(2)]
b = sorted(a)
for i in range(n):
    if i % 2:
        d[0][a[i]] += 1
        d[1][b[i]] += 1
t1 = 0
t2 = 0
for v1, v2 in zip(d[0].values(), d[1].values()):
    if v1 > v2:
        t1 += v1 - v2
print(t1)

Solution (Python):
N = int(input())
ans = 0
if N % 2 == 1:
    A = [0]*N
    for i in range(N):
        A[i] = int(input())
else:  
    N += 1
    A = [0] * N
    A[N-1] = 10**9+1
    for p in range(N-1):
        A[p] = int(input())
even = set()
for k in range(N//2+1):
    even.add(A[2*k])

B = sorted(A)
for j in range(N // 2):
    if B[(2 * j)+1] in even:
        ans += 1
        

print(ans)

Solution (Python):

n = int(input())
a = [[] for i in range(n)]
for i in range(n):
    tmp = [int(input()), i]
    a[i] = tmp

b = sorted(a)


c = []
ans = 0
for i in range(n):
    c.append(b[i][1])
    ans += (i - c[i])%2
ans //= 2

print(ans)

Solution (Python):
import bisect

def main():
    n = int(input())
    l = [[i,int(input())] for i in range(n)]
    l.sort(key=lambda x:x[1])
    res =0
    for i in range(n):
        if i % 2 != l[i][0] % 2:
            res += 1
    print(res // 2)


main()

Solution (Python):
import math,string,itertools,fractions,heapq,collections,re,array,bisect,sys,random,time,queue,copy

sys.setrecursionlimit(10**7)
inf=10**20
mod=10**9+7
dd=[(-1,0),(0,1),(1,0),(0,-1)]
ddn=[(-1,0),(-1,1),(0,1),(1,1),(1,0),(1,-1),(0,-1),(-1,-1)]

def LI(): return [int(x) for x in sys.stdin.readline().split()]
def LI_(): return [int(x)-1 for x in sys.stdin.readline().split()]
def I(): return int(sys.stdin.readline())
def LS(): return sys.stdin.readline().split()
def S(): return input()

def main():
  n=I()
  l=[]

  for i in range(n):
    l.append([i,I()])

  l2=copy.deepcopy(l)

  l2=sorted(l2,key=lambda x:x[1])

  ans=0
  for i,x in enumerate(l2):
    if i%2!=x[0]%2:
      ans+=1
  return ans//2


print(main())

Solution (Python):
n = int(input())
a = [int(input()) for _ in range(n)]
print(len(set(a[::2]) ^ set(sorted(a)[::2])) // 2)

Solution (Python):
n=int(input())
A = [0]*(n)
for i in range(n):
    s=int(input())
    A[i]=[s,i]    
lista=sorted(A,key=lambda x:x[0])
cnt=0
for i in range(n):
    lista[i].append(i)
for i in range(n):
    if (lista[i][1]-lista[i][2])%2!=0:
        cnt+=1
print(cnt//2)

Solution (Python):



def main():
    n = int(input())
    a = [int(input()) for _ in range(n)]
    before = list()
    after = list()

    
    
    
    for index, ai in enumerate(a, 1):
        before.append((ai, index % 2))

    for index, ai in enumerate(sorted(a), 1):
        after.append((ai, index % 2))

    count = 0

    for b, a in zip(sorted(before), after):
        if b[1] != a[1]:
            count += 1

    
    print(count // 2)


if __name__ == '__main__':
    main()

Solution (Python):
n,*a=map(int,open(0).read().split())
print(len(set(a[::2])^set(sorted(a)[::2]))//2)

Solution (Python):
N = int(input())

A = []

for i in range(N):
    a = int(input())
    A.append([a, i+1])

A.sort()

for i in range(N):
    A[i].append(i+1)


ans = 0
for i in range(N):
    num, before, after = A[i]
    if before % 2 != after % 2:
        ans += 1

print(ans//2)

Solution (Python):


import sys

inpt=sys.stdin.readline
n=int(input())
a=[]
for i in range(n):
    a.append((int(input()),i+1))
a.sort()

cnt=0
for idx,aa in enumerate(a,1):
    if aa[1]%2==idx%2:continue
    cnt+=1
print(cnt//2)

Solution (Python):
N = int(input())
A = [[i%2, int(input())] for i in range(N)]
A = sorted(A,key=lambda x: x[1])

cnt = 0
for i in range(N) :
    if A[i][0] != i%2 :
        cnt += 1

ans = cnt // 2
print(ans)