#!/usr/bin/perl
use strict;
use warnings;

my $s='IIIIIIIIIIIIIIIIIIIIIIIIIIOOOOOSSSSS';

if (0 == $s =~ tr/[IOSM]//c) {
    print "case1\n";
}

elsif (0 == $s =~ tr/[IOS]//c) {
    print "case2\n";
}