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 Lua (5.3.2) (judge verdict: Accepted)

local function str2tbl(s)
    local t = {string.byte(s, 1, #s)}
    for i=1, #t do
        t[i] = string.char(t[i])
    end
    return t
end

local function each_char2(s)
    return ipairs(str2tbl(s))
end

local function each_char(s)
    local f = function(_, i)
        i = i + 1
        if i <= #s then
            return i, string.sub(s, i, i)
        end
    end
    return f, nil, 0
end

function string.at(s, i)
    return string.sub(s, i, i)
end

-- C
local S = {}
while true do
    local c = io.read(1)
    if c == "1" then
        table.insert(S, 1)
    elseif c == "0" then
        table.insert(S, 0)
    else
        break
    end
end
local oddeven_01, oddeven_10 = 0, 0
for i=1,#S do
    local x = S[i]
    if i & 1 == 1 then
        -- odd
        if x == 1 then
            oddeven_01 = oddeven_01 + 1
        elseif x == 0 then
            oddeven_10 = oddeven_10 + 1
        end
    else
        -- even
        if x == 1 then
            oddeven_10 = oddeven_10 + 1
        elseif x == 0 then
            oddeven_01 = oddeven_01 + 1
        end
    end
end
local min = oddeven_01
if min > oddeven_10 then
    min = oddeven_10
end
print(min)