#include<stdio.h>
#include<string.h>
#include<ctype.h>
#define MAX 100
int 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 evaluate(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=='/'){
            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 expr[MAX];
    if(!fgets(expr,sizeof(expr),stdin)){
        printf("Invalid input\n");
        return 0;
    }
    int result=evaluate(expr);
    if(result==-9999)
}