int match (char* s) {
    int pos = -1;
    int state = 1;
    int done = -1;

    while (1) {
        char c;
        c = s[++pos];
        if (state == 4) {
            done = pos;
            if (c == '\0') break;
            if (c == 'a') {
                state = 4;
                continue;
            }
            if (c == 'b') {
                state = 4;
                continue;
            }
            break;
        }
        if (state == 1) {
            if (c == '\0') break;
            if (c == 'a') {
                state = 2;
                continue;
            }
            if (c == 'b') {
                state = 3;
                continue;
            }
            break;
        }
        if (state == 3) {
            if (c == '\0') break;
            if (c == 'a') {
                state = 2;
                continue;
            }
            if (c == 'b') {
                state = 4;
                continue;
            }
            break;
        }
        if (state == 2) {
            if (c == '\0') break;
            if (c == 'a') {
                state = 4;
                continue;
            }
            if (c == 'b') {
                state = 3;
                continue;
            }
            break;
        }
        fprintf( stderr, "error: Unknown state: %d", state );
        exit(2);
    }
    return done;
}