Problem:
Score : 300 points

Problem Statement

N tiles are arranged in a row from left to right. The initial color of each tile is represented by a string S of length N.

The i-th tile from the left is painted black if the i-th character of S is 0, and painted white if that character is 1.

You want to repaint some of the tiles black or white, so that any two adjacent tiles have different colors.

At least how many tiles need to be repainted to satisfy the condition?

Constraints

1 \leq |S| \leq 10^5

S_i is 0 or 1.

Input

Input is given from Standard Input in the following format:

S

Output

Print the minimum number of tiles that need to be repainted to satisfy the condition.

Sample Input 1

000

Sample Output 1

1

The condition can be satisfied by repainting the middle tile white.

Sample Input 2

10010010

Sample Output 2

3

Sample Input 3

0

Sample Output 3

0

Solution in PyPy3 (2.4.0) (judge verdict: Accepted)

import sys, re, os
from collections import deque, defaultdict, Counter
from math import ceil, sqrt, hypot, factorial, pi, sin, cos, radians, acos, atan, asin, log, log10
from itertools import permutations, combinations, product, accumulate
from operator import itemgetter, mul
from copy import deepcopy
from string import ascii_lowercase, ascii_uppercase, digits
from fractions import gcd
def debug(*args):
    if debugmode:
        print(*args)
def input(): return sys.stdin.readline().strip()
def STR(): return input()
def INT(): return int(input())
def FLOAT(): return float(input())
def MAP(): return map(int, input().split())
def S_MAP(): return map(str, input().split())
def LIST(): return list(map(int, input().split()))
def S_LIST(): return list(map(str, input().split()))
def lcm(a, b): return a * b // gcd(a, b)
sys.setrecursionlimit(10 ** 9)
inf = sys.maxsize
mod = 10 ** 9 + 7
dx = [0, 0, 1, -1, 1, -1, -1, 1]
dy = [1, -1, 0, 0, 1, -1, 1, -1]
debugmode = True

s = [int(i) for i in STR()]
flag = False
ans = 0
for i in range(1, len(s)):
    if s[i] == s[i - 1]:
        s[i] = int(not s[i - 1])
        if flag:
            flag = False
            ans += 1
        else:
            flag = False
            ans += 1
    if flag:
        ans += 1
print(ans)