// editor3
#include<stdio.h>
#include<string.h>
#include<ctype.h>
#define max 100
char stack[max][max];
int top=-1;

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

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

char* prefixtopostfix(char str[]){
    char ch;
    int length=strlen(str);
    int chlen;
    for(int i=length;i>=0;i--){
        ch=str[i];
        if(isalnum(ch)){
            char temp[2];
            temp[0]=ch;
            temp[1]="\0";
            push(temp);
        }
        else if(!(ch=='+')){
            printf("Invalid input");
            return 0;
        }
        else{
            char op1[max],op2[max],res[max];
            strcpy(op1,pop());
            strcpy(op2,pop());
            strcat(res,op2);
            strcat(res,op1);
            chlen=strlen(res);
            res[chlen]=ch;
            res[chlen+1]="\0";
            push(temp);
        }
    }
}

int main(){
    char prefix[max];
    scanf(" %s",prefix);
    prefixtopostfix(prefix);
    return 0;
}