#include <iostream>
#include <stack>
#include <string>

int main() {
    bool wasGlobal = false;
    std::stack<std::string> programStack;
    std::string s, tmp, answer = "YES";

    getline(std::cin, s);

    for (int i = 0; i < s.size(); ++i) {
        if (s[i] == '<') {
            tmp.clear();

            int j = i + 1;
            bool isOpen = true;
            bool isCorrectClosed = false;

            if (s[j] == '/') {
                isOpen = false;
                j++;
            }
            while (j < s.size() && s[j] != '>') {
                tmp += s[j++];
            }
            if (j < s.size() && s[j] == '>') {
                isCorrectClosed = true;
            }
            if (!isCorrectClosed) {
                answer = "NO";
                break;
            }
            if (isOpen) {
                if (programStack.empty() && wasGlobal) {
                    answer = "NO";
                    break;
                }
                wasGlobal = true;
                programStack.push(tmp);
            } else {
                if (programStack.empty() || programStack.top() != tmp) {
                    answer = "NO";
                    break;
                }
                programStack.pop();
            }
            i = j;
        } else {
            if (programStack.empty()) {
                answer = "NO";
                break;
            }
        }
    }
    if (!programStack.empty() || s.empty()) {
        answer = "NO";
    }
    std::cout << answer;
    return 0;
}