Alex

set st [gets stdin]
 set n [string length $st]
 set s [split $st {}]
 set i 0
 set ok 1
 set count 0
 foreach c $s {
     set i [expr {$i + 1}]

     #puts $c

     if {$ok == 1} {
         set tmp 0
         set dot 0
         if {"a" <= $c && $c <= "z"} {
             #puts -nonewline "letter "
             set tmp 1
             set dot 0
         }
         if {"0" <= $c && $c <= "9"} {
             #puts -nonewline "digit "
             set tmp 1
             set dot 0
         }
         if {$c == "."} {
             #puts -nonewline "dot "
             set tmp 1
             set dot 1
         }
         if {$tmp == 0} {
             set ok 0
         }
         if {$ok == 1} {
             if {$count == 0 && $dot != 0} {
                 set ok 0
             }
             if {$ok == 1 && $dot == 0} {
                 set count [expr {$count + 1}]
             }
             if {$ok == 1 && $dot != 0} {
                 set count 0
             }
            #puts -nonewline $ok
            #puts -nonewline " "
            #puts -nonewline $count
            #puts -nonewline " "
            #puts -nonewline $dot
            #puts ""
         }
     }

 }
 if {$count < 2 || $count > 3} {
     set ok 0
     # puts "OLOLO"
 }
 if {$ok == 1} {
     puts "YES"
 }
 if {$ok == 0} {
     puts "NO"
 }