#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <math.h>
#include <string.h>

/* The C Programming Language: 2nd Edition
 *
 * Exercise 7-5: Rewrite the postfix calculator of Chapter 4 to use scanf
 * and/or sscanf to do the input and number conversion.
 *
 * Notes:
 * scanf wants allocated memory of some sort, meaning you're either going
 * to pass it a pointer (with malloc()'d memory) or you're passing a variable
 * with the unary & (address-of) operator. Failing to use scanf correctly
 * _will_ create runtime problems! gcc won't tell you what happens without
 * -Wall and -Wextra, but scanf segfaults by trying to access an uninitialized
 * pointer.
 *
 * Thus there are two ways to use scanf:
 *
 * int foo = 0;
 * scanf("%d", &foo);
 * // do stuff
 *
 * -- or --
 *
 * int *foo = malloc(sizeof(int));
 * scanf("%d", foo);
 * // do stuff
 * free(foo);
 *
 * For the sake of sanity in an easy exercise, I'll be using the former form
 * since a few values on the stack won't hurt anything.
 */

#define MAXOP    100
#define MAXVAL   100
#define BUFSIZE  100

void push(double);
double pop(void);

int sp = 0; // Next free stack position
double val[MAXVAL]; // Value stack
char buf[BUFSIZE]; // buffer
int bufp = 0; // next free position in buf
double vars[27];

/* Reverse Polish calculator:
 *
 * Binary operations (+-*\)
 *     operand operand operator
 *
 * Example: 6 minus 2 in Reverse Polish Notation is "6 2 -"
 */
int main() {
	char *c;
	double a = 0, op2;
	char s[MAXOP];
	char ltr = '\0';
	while (scanf("%s%c", s, &ltr) == 2) {
		if (sscanf(s, "%lf", &a) == 1) {
			push(a);
		} else if (sscanf(s, "%s", buf)) {
			for (c = buf; *c; c++) {
				switch (*c) {
					case '+':
						push(pop() + pop());
						break;
					case '*':
						push(pop() * pop());
						break;
					case '-':
						op2 = pop();
						push(pop() - op2);
						break;
					case '/':
						op2 = pop();
						if (op2 != 0.0) {
							push(pop() / op2);
						} else {
							printf("Error: Cannot divide by zero.\n");
						}
						break;
					default:
						printf("Error: Unknown command %s\n", s);
						break;
				}
			}
			if (ltr == '\n') {
				printf("%.8f\n", pop());
			}
		}
	}
	return 0;
}

void push(double f) {
	if (sp < MAXVAL) {
		val[sp++] = f;
	} else {
		printf("Error: Stack full. Cannot push %g\n", f);
	}
}

double pop(void) {
	if (sp > 0) {
		return val[--sp];
	} else {
		printf("Error: Stack empty.\n");
		return 0.0;
	}
}