#include <cstdio>
#include <cctype>
#include <cstring>

char S[1024];

int main() {
    //freopen("test.in", "r", stdin);
    
    while (true) {
        bool hasB = false;
        bool hasI = false;
        bool hasV = false;
        int nrp = 0;
        int i;
        fgets(S+1, 1024, stdin);
        S[0] = '[';
        if (S[strlen(S)-1] == '\n') S[strlen(S)-1] = ']';
            else S[strlen(S)] = ']';
        for (i=0; S[i]!='\0' && S[i] !='\n'; ++i) {
            //printf("%c", S[i]);
            if (tolower(S[i]) == 'b' && (tolower(S[i+1])=='x' || tolower(S[i+1])=='p')) {
                ++i;
                if (hasB) break;
                hasB = true;
            }
            else
                if (tolower(S[i+1]) == 'i' && (tolower(S[i])=='s' || tolower(S[i])=='d')) {
                    ++i;
                    if (hasI) break;
                    hasI = true;
                }
            else
            if ('a' <= S[i] && S[i] <= 'z') {
                if (isdigit(S[i+1]) || isalpha(S[i+1])) break;
                if (hasV) break;
                hasV = true;
            }
            else
            if (S[i] == '+' || S[i] == '-') {
                if (i == 0 || S[i-1] == '[' || S[i+1] == '\0' || S[i+1] == ']') break;
            }
            else
            if (S[i] == '[') ++nrp;
            else
            if (S[i] == ']') {
                --nrp;
                if (nrp < 0) break;
            }
            else if (S[i] < '0' || S[i] > '9') {
                if (isdigit(S[i+1]) || isalpha(S[i+1])) break;
            }
        }
        
        if ((S[i] == '\0' || S[i] == '\n') && nrp == 0) printf("OK\n");
        else printf("ERROR\n");

        if (feof(stdin)) return 0;

    }
    
    return 0;
}