BEGIN {
    stack[0] = 0
	stack_p = 0

	print rpn_calc("3 19 + -2 /")
	print rpn_calc("3 19 + -2 / +")
	print rpn_calc("1 2 + 3 4 5 sum")
	print rpn_calc("5 4 - exp")
	print rpn_calc("1 2.0 +")
	print rpn_calc("12 5 /")
	print rpn_calc("2 3 4 prod")
}

function rpn_calc(str,  i, n, q, ql, t) {

	ql = split(str, q)
	if (! is_integer(q[1])) return 0
	n = q[1]

	init()
	for(i = 2; i <= ql; i++) {
		t = q[i]
		if (is_integer(t)) {
			push(n)
			n = t
		}
		else if (t == "+") {
			if (empty()) return 0
			n += pop()
		}
		else if (t == "-") {
			if (empty()) return 0
			n = pop() - n
		}
		else if (t == "*") {
			if (empty()) return 0
			n *= pop()
		}
		else if (t == "/") {
			if (empty()) return 0
			n = int(pop() / n)
		}
		else if (t == "exp") {
			n = exp(n)
		}
		else if (t == "sum") {
			while(! empty()) {
				n += pop()
			}
		}
		else if (t == "prod") {
			while(! empty()) {
				n *= pop()
			}
		}
		else {
			return "error"
		}
	}

	return n
}

function is_integer(s) {
	return match(s, /^-?(0|[1-9][0-9]*)$/)
}

function init( n) {
	stack_p = 0
}

function push(n) {
	stack[stack_p++] = n
}

function empty( n) {
	return (stack_p < 1);
}

function pop( n) {
	return (empty() ? 0 : stack[--stack_p])
}