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