#!/usr/bin/env bash

paste -s -d '' input.txt | 
  perl -lne '
    print "$1$4$2$3" 
    while 
      /(?<=(.).)(?<=(.).{138})A(?=.{138}(.))(?=.(.))/g
  ' | 
  grep -Eo '(SM|MS){2}' | 
  wc -l