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

#define MAX 1000

typedef struct {
    char *arr[MAX];
    int top;
}Stack;

void init(Stack *s){
    s->top = -1;
}

int isEmpty(Stack *s){
    return s->top == -1;
}

void push(Stack *s,char *val){
    s->arr[++(s->top)]=val;
}

char *pop(Stack *s){
    if(isEmpty(s)) return NULL;
    return s->arr[(s->top)--];
}

int isOperator(char c){
    return (c =='+' || c =='-' || c =='*' || c =='/');
}

int validParentheses(char *expr){
    int count = 0;
    for(int i=0;expr[i];i++){
        if(expr[i] == '(') count++;
        else if(expr[i] == ')') count--;
        if(count < 0) return 0;
    }
    return count == 0;
}

int validCharacters(char *expr){
    for(int i=0;expr[i];i++){
        if(!isalnum(expr[i]) && !isOperator(expr[i]) && expr[i] != '(' && expr[i] != ')' && expr[i] !='')
        return 0;
    }
    return 1;
}

int main(){
    char expr[MAX];
    fgets(expr,MAX,stdin);
    expr[atrcspn(expr,"\n")] = 0;
    
    if(!validParentheses(expr) || !validCharacters(expr)){
        printf("Invalid input\n");
        return 0;
    }
    
    Stack stack;
    init(&stack);
    
    int len = strlen(expr);
    
    for(int i=len-3;i>=0;i--){
        if(expr[i] == '') continue;
        
        if(isalnum(expr[i])){
            char *operand = (char*) malloc(2);
            operand[0] = expr[i];
            operand[1] = '\0';
            push(&stack,operand);
        }
        else if(isOperator(expr[i])){
            char *op1 = pop(&stack);
            char *op2 = pop(&stack);
            if(!op1 || !op2){
                printf("Invalid input");
                return 0;
            }
            char *newExpr = (char *) malloc (strlen(op1) + strlen(op2) + 2);
            sprintf(newExpr, "%s%s%c",op1,op2,expr[i]);
            push(&stack,newExpr);
        }
    }
    if(stack.top != 0){
        printf("Invalid input\n");
        return 0;
    }
    printf("%s\n",stack.arr[stack.top]);
    return 0;
}