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

int main(){
    char expr[MAX];
    fgets(expr,MAX,stdin);
    expr[strcspn(expr,"\n")] = 0;
    
    if(!validparentheses(expr) || validcharacters(expr)){
        printf("Invalid input");
        return 0;
    }
    
    Stack stack;
    init(&stack);
    
    int len = strlen(expr);
    
    for(int i=len-1; 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]);
            psuh(&stack,newexpr);
        }
    }
    
    if(stack.top!=0){
        printf("Invalid input");
        return 0;
    }
    
    printf("%s\n",stack.arr[stack.top]);
    return 0;
}