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

#define MAX 100

int evaluate(const char *sequence) {
    int stack[MAX], top = -1;
    int len = strlen(sequence);

    for (int i = len - 1; i >= 0; i--) {
        char ch = sequence[i];

        if (isdigit(ch)) {
            stack[++top] = ch - '0';
        } else if (ch == '+' || ch == '-' || ch == '*' || ch == '/') {
            if (top < 1) return -1; 

            int a = stack[top--];
            int b = stack[top--];
            int result;

            switch (ch) {
                case '+': result = a + b; break;
                case '-': result = a - b; break;
                case '*': result = a * b; break;
                case '/': 
                    if (b == 0) return -1;
                    result = a / b; 
                    break;
            }
            stack[++top] = result;
        } else {
            return -1;
        }
    }

    return (top == 0) ? stack[top] : -1; 
}

int main() {
    char sequence[MAX];
    scanf("%s", sequence);

    int result = evaluate(sequence);
    if (result ==