import sys read = sys.stdin.buffer.read readline = sys.stdin.buffer.readline readlines = sys.stdin.buffer.readlines class BinaryIndexedTree(): def __init__(self, seq): self.size = len(seq) self.depth = self.size.bit_length() self.build(seq) def build(self,seq): data = seq size = self.size for i,x in enumerate(data): j = i+(i&(-i)) if j < size: data[j] += data[i] self.data = data def __repr__(self): return self.data.__repr__() def get_sum(self,i): data = self.data s = 0 while i: s += data[i] i -= i & -i return s def add(self, i, x): data = self.data size = self.size while i < size: data[i] += x i += i & -i def find_kth_element(self,k): data = self.data; size = self.size x,sx = 0,0 dx = 1 << (self.depth) for i in range(self.depth - 1, -1, -1): dx = (1 << i) if x + dx >= size: continue y = x + dx sy = sx + data[y] if sy < k: x,sx = y,sy return x + 1 def Inversion(seq): # seqは、1,2,...,Nの順列 N = len(seq) bit = BinaryIndexedTree([0] * (N+1)) inv = N*(N-1)//2 for x in seq: inv -= bit.get_sum(x) bit.add(x,1) return inv N,*A = map(int,read().split()) x = Inversion(A) print(x)