#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>

#define STACK_SIZE 10

float stack[STACK_SIZE];
int stack_top = -1;

bool is_number(char *string) {
    char *end;
    strtof(string, &end);
    return end != string && *end == '\0';
}

bool is_operation(char *string) {
    return strlen(string) == 2 && (string[0] == '+' || string[0] == '-' || string[0] == '*' || string[0] == '/');
}

float calculator(float n1, float n2, char operation) { 
    if (operation == '+') {
        return n1 + n2;
    }
    else if (operation == '-') {
        return n1 - n2;
    }
    else if (operation == '*') {
        return n1 * n2;
    }
    else if (operation == '/') {
        if (n2 != 0) {
            return n1 / n2;
        } else {
            printf("Error: division by zero\n");
            exit(1);
        }
    }
    return 0;
}

void push(float number) {
    if (stack_top < STACK_SIZE - 1) {
        stack[++stack_top] = number;
    } else {
        printf("Error: stack overflow\n");
        exit(1);
    }
}

float pop() {
    if (stack_top >= 0) {
        return stack[stack_top--];
    } else {
        printf("Error: stack is empty\n");
        exit(1);
    }
}

int main() {
    char arr[50];
    char *pend;
    stack_top = -1;

    while (fgets(arr, 50, stdin)) {
        if (arr[0] == '\n' || arr[0] == EOF) {
            break;
        }

        if (is_number(arr)) {
            float number = strtof(arr, &pend);
            push(number);
            printf("Number added: %.2f\n", number);
        }
        else if (is_operation(arr)) {
            if (stack_top < 1) {
                printf("Error: not enough numbers in the stack for operation\n");
                return 1;
            }

            float n2 = pop();
            float n1 = pop();
            char operation = arr[0];
            float result = calculator(n1, n2, operation);
            push(result);
            printf("Operation result: %.2f\n", result);
        }
        else {
            printf("Error: invalid input\n");
            return 1;
        }
    }

    if (stack_top == 0) {
        printf("Final result: %.2f\n", pop());
    } else {
        printf("Error: stack contains more than one number after operations\n");
    }

    return 0;
}