#include<stdio.h>
#include<string.h>
#include<ctype.h>
#define MAX 100
char stack [MAX];
int top = -1;
void push(int val){
    if(top < MAX - 1){
        stack[++top] = val;
    }
}
int pop(){
    if(top >=0){
        return stack[top--];
    }
    return -9999;
}
int evaluvate(char *exp){
    int len = strlen(exp);
    for(int i = len - 1; i >= 0; i--){
        char c = exp[i];
        if(isspace(c))continue;
        if(isdigit(c)){
            push(c - '0');
        }
        else if(c == '+' || c == '-' || c == '*' || c == '/'){
            if(top < 1) return -9999;
            int a = pop();
            int b = pop();
            int result;
            switch (c){
                case'+':result = a + b; break;
                case'-':result = a - b;break;
                case'*':result = a * b;break;
                case '/':
                        if(b == 0)return -9999;
                        result = a / b;
                        break;
                        default : return -9999;
            }
            push(result);
        }
        else{
            return -9999;
        }
    }
    if(top != 0)return -9999;
    return pop();
}
int main(){
    char exp[MAX];
    if(!fgets(exp,sizeof(expr),stdin)){
        printf("Invalid input\n");
        return 0;
    }
    int result = evaluvate(expr);
    if(result == -9999){
        printf("Invalid input\n");
    }
    else{
        printf("%d\n",result);
    }
        return 0;
}