output_description: If a tree with n vertices that satisfies the conditions does not exist, print
  `-1`.
  
  If a tree with n vertices that satisfies the conditions exist, print n-1
  lines. The i-th line should contain u_i and v_i with a space in between. If
  there are multiple trees that satisfy the conditions, any such tree will be
  accepted.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      s
attempt: input()
  print(input().split().index("1") + 1)
  
problem_description: Statement
  
  You are given a string s of length n. Does a tree with n vertices that
  satisfies the following conditions exist?
  
    * The vertices are numbered 1,2,..., n.
    * The edges are numbered 1,2,..., n-1, and Edge i connects Vertex u_i and v_i.
    * If the i-th character in s is `1`, we can have a connected component of size i by removing one edge from the tree.
    * If the i-th character in s is `0`, we cannot have a connected component of size i by removing any one edge from the tree.
  
  If such a tree exists, construct one such tree.
samples: [{"input": "1111", "output": "-1\n    \n\nIt is impossible to have a connected component of size n after removing one\nedge from a tree with n vertices.\n\n* * *"}, {"input": "1110", "output": "1 2\n    2 3\n    3 4\n    \n\nIf Edge 1 or Edge 3 is removed, we will have a connected component of size 1\nand another of size 3. If Edge 2 is removed, we will have two connected\ncomponents, each of size 2.\n\n* * *"}, {"input": "1010", "output": "1 2\n    1 3\n    1 4\n    \n\nRemoving any edge will result in a connected component of size 1 and another\nof size 3."}]