while line=gets
    while !(line=~/(the|this|that)/)
        for i in 0..line.size-1
            if (line[i]=~/[a-z]/)
                if (line[i]=~/z/)
                    line[i]='a'
                else
                    line[i]=line[i].succ
                end
            end
        end
    end
    puts line
end