#!/opt/chipster/tools/Python-2.7.12/bin/python

"""
Read a MAF from standard input and determine the mean length of ungapped pieces
in each block.

usage: %prog < maf > out
"""
from __future__ import division, print_function

import sys

import bx.align.maf


def main():
    
    for m in bx.align.maf.Reader( sys.stdin ):  
    
        ungapped_columns = 0
        ungapped_runs = 0
        in_ungapped = False
        
        for col in m.column_iter():
            is_gap = ( '-' in col )
            if not is_gap: ungapped_columns += 1
            if in_ungapped and is_gap:
                ungapped_runs += 1
            in_ungapped = not is_gap
        if in_ungapped: ungapped_runs += 1

        print(ungapped_columns / ungapped_runs)


if __name__ == "__main__":
    main()