#include <iostream>
#include <fstream>
#include <cctype>
#include <cstring>
using namespace std;

char upc(char c){
    if(c>='a'&&c<='z') c=c-'a'+'A';
    return c;
}

char s[150];
int ind;

bool was_index;
bool was_base;
bool was_variable;

bool term(){
    if(upc(s[ind]) == 'B' && (upc(s[ind+1])=='X'||upc(s[ind+1])=='P') ){
        if(was_base) return false;
        else{
            ind+=2;
            was_base=true;
            return true;
        }
    }
    else if( (upc(s[ind]) == 'S' || upc(s[ind])=='D') && upc(s[ind+1])=='I'){
        if(was_index) return false;
        else{
            ind+=2;
            was_index=true;
            return true;
        }
    }
    else if(s[ind]>='a'&&s[ind]<='z'){
        if(was_variable) return false;
        else{
            ind++;
            was_variable=true;
            return true;
        }

    }
    else if(isdigit(s[ind])){
        while(isdigit(s[ind])) ++ind;
        return true;
    }
    else return false;
}

bool expr(){
    int got_term1=false;

    if(s[ind]=='['){
        ++ind;
        if(!expr()) got_term1=false;
        else if(s[ind]!=']') got_term1=false;
        else{ ++ind; got_term1=true;}
    }
    else got_term1=term();

    if(!got_term1) return false;
    else{
        bool got_op=false;
        while(s[ind]=='+'||s[ind]=='-'){ got_op=true; ++ind; }
        if(s[ind]=='[') got_op=true;

        if(!got_op) return true;
        else return expr();
    }


}


int main()
{
    while(cin.getline(s,150) && strlen(s)>0){
        ind=0;
        was_index=was_base=was_variable=false;
        if(expr()&&s[ind]=='\0') cout<<"OK\n";
        else cout<<"ERROR\n";
    }
}