#include<cstdio>
#include<cstring>
using namespace std;
char a[105];
int n,i,b,s,l,cnt,plm;
int main()
{
	//freopen("test.in","r",stdin);
	//freopen("test.out","w",stdout);
    while(fgets(a+1,105,stdin))
    {
        n=strlen(a+1)-1; a[0]='['; a[n+1]=']';
        b=0;s=0;l=0;cnt=0;
        for(i=1;i<=n;i++)
        {
            if(a[i]=='B' || a[i]=='b')
            {
                //if(a[i-1]!='[' && a[i-1]!='+' && a[i-1]!='-') {printf("ERROR\n"); break;}
                if(a[i+1]=='X' || a[i+1]=='x' || a[i+1]=='P' || a[i+1]=='p')
                {
                    if(!b) {b=1; i++;}
                    else {printf("ERROR\n"); break;}
                }
                else
                {
                    if(a[i]=='b')
                    {
                        if(!l) l=1;
                        else {printf("ERROR\n"); break;}
                    }
                    else {printf("ERROR\n"); break;}
                }
            }
            else if(a[i]=='S' || a[i]=='s' || a[i]=='D' || a[i]=='d')
            {
                //if(a[i-1]!='[' && a[i-1]!='+' && a[i-1]!='-') {printf("ERROR\n"); break;}
                if(a[i+1]=='I' || a[i+1]=='i')
                {
                    if(!s) {s=1; i++;}
                    else {printf("ERROR\n"); break;}
                }
                else
                {
                    if(a[i]=='s' || a[i]=='d')
                    {
                        if(!l) l=1;
                        else {printf("ERROR\n"); break;}
                    }
                    else {printf("ERROR\n"); break;}
                }
            }
            else if(a[i]>='a' && a[i]<='z')
            {
                //if(a[i-1]!='[' && a[i-1]!='+' && a[i-1]!='-') {printf("ERROR\n"); break;}
                if(!l) l=1;
                else {printf("ERROR\n"); break;}
            }
            else if(a[i]>='0' && a[i]<='9')
            {
                //if(a[i-1]!='[' && a[i-1]!='+' && a[i-1]!='-') {printf("ERROR\n"); break;}
            }
            else if(a[i]=='+' || a[i]=='-')
            {
                if(a[i-1]=='[' || a[i+1]==']') {printf("ERROR\n"); break;}
            }
            else if(a[i]=='[')
            {
                cnt++;
            }
            else if(a[i]==']')
            {
                if(a[i-1]=='[') {printf("ERROR\n"); break;}
                if(cnt) cnt--;
                else {printf("ERROR\n"); break;}
            }
            else {printf("ERROR\n"); break;}
        }
        if(i==n+1)
        {
            if(cnt==0) printf("OK\n");
            else printf("ERROR\n");
        }
    }
	return 0;
}