Problem:
Score : 100 points

Problem Statement

Snuke prepared 6 problems for a upcoming programming contest.
For each of those problems, Rng judged whether it can be used in the contest or not.

You are given a string S of length 6.
If the i-th character of s is 1, it means that the i-th problem prepared by Snuke is accepted to be used; 0 means that the problem is not accepted.

How many problems prepared by Snuke are accepted to be used in the contest?

Constraints

The length of S is 6.

S consists of 0 and 1.

Inputs

Input is given from Standard Input in the following format:

S

Outputs

Print the number of problems prepared by Snuke that are accepted to be used in the contest.

Sample Input 1

111100

Sample Output 1

4

The first, second, third and fourth problems are accepted, for a total of four.

Sample Input 2

001001

Sample Output 2

2

Sample Input 3

000000

Sample Output 3

0

Solution in Ruby (2.3.3) (judge verdict: Runtime Error)

N, W = gets.chomp.split(' ').map(&:to_i)
A, B = []

0.upto(N-1) do |i|
  A[i], B[i] = gets.chomp.split(' ').map(&:to_i)
end

def solve
  res = 0
  if i == N
    res = 0
  elsif j < A[i]
    res = solve(i + 1, j)
  else
    res = [ solve(i + 1, j), solve(i + 1, j - A[i]) + B[i] ].max
  end
  res
end

puts "#{solve(0, W)}