#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=='('||ch==')');
}
void fun(ch*str){
    int len = strlen(str),ind;
    for(ind=len-1;ind>=0;ind--){
        char ch = str[ind];
        if(!isvalid(ch)){
            printf("Invalid input");
        }
        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, pop());
            int l = 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;
}