#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<ctype.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 isOp(char c){
    return (c=='+' || c=='-' || c=='*' || c=='/');
}
int validP(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 validC(char*expr){
    for(int i=0;expr[i];i++){
        if(!isalnum(expr[i] && !isOp(expr[i] && 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(!validP(expr)|| !validC(expr)){
        printf("Invalid input\n");
        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\n");
            return 0;
        }
        char *newExpr = (char*)malloc(strlen(op1)+strlen(op2)+2);
        printf(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;
}