static box StringUtils {
    is_digit(ch) {
        return ch == "0" or ch == "1" or ch == "2" or ch == "3" or ch == "4"
            or ch == "5" or ch == "6" or ch == "7" or ch == "8" or ch == "9"
    }

    is_integer(s) {
        if s.length() == 0 {
            return false
        }

        local start = 0
        if s.substring(0, 1) == "-" {
            if s.length() == 1 {
                return false
            }
            start = 1
        }

        local i = start
        loop(i < s.length()) {
            if not this.is_digit(s.substring(i, i + 1)) {
                return false
            }
            i = i + 1
        }
        return true
    }
}

static box Main {
    main() {
        return StringUtils.is_integer("123") ? 7 : 1
    }
}