#include<stdio.h>
#include<ctype.h>
#include<string.h>
#define max 25
char stack[max][max];
int top=-1;

void push(char ch[]){
    strcpy(stack[++top],ch);
}

char*pop(){
    return stack[top--];
}

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

void fun(char *str){
    int len strlen(str),i;
    for(i=len-1;i>=0;i--){
        char ch=str[i];
        if(isValid(ch)){
            printf("Invalid input");
            return 0;
        }
        if(isalnum(ch)){
            char temp[2];
            temp[0]=ch;
            temp[1]='\0';
            push(temp);
        }
        else if(isOperator(ch)){
            char opd1[max],opd2[max],res[max];
            strcpy(opd1,pop());
            strcpy(opd2,pop());
            strcpy(res,opd1);
            strcpy(res,opd2);
            int l=strlen(res);
            res[l]=ch;
            res[l+1]='\0';
            push(res);
        }
    }
    printf("%s",stack[top]);
}
int main(){
    char str[max];
    scanf("[^\n]s",str);
    fun(str);
    return 0;
}