procedure evalRPN(string s)
sequence stack = {}
sequence ops = split(s)
    for i=1 to length(ops) do
        string op = ops[i]
        switch op
            case "+": stack[-2] = stack[-2]+stack[-1]; stack = stack[1..-2]
            case "-": stack[-2] = stack[-2]-stack[-1]; stack = stack[1..-2]
            case "*": stack[-2] = stack[-2]*stack[-1]; stack = stack[1..-2]
            case "/": stack[-2] = stack[-2]/stack[-1]; stack = stack[1..-2]
            case "^": stack[-2] = power(stack[-2],stack[-1]); stack = stack[1..-2]
            default : stack = append(stack,scanf(op,"%d")[1][1])
        end switch
        ?{op,stack}
    end for
end procedure
evalRPN("3 4 2 * 1 5 - 2 3 ^ ^ / +")