С (Region 2012)

#include <cstdio>
#include <iostream>
#include <string>

#define N 1005

using namespace std;

string temp = "<>/", s, st[N];
int top;

bool check() {
    top = 0;
    for (int i = 0; i < s.size();) {
        if (s[i] != '<')
            return false;
        int j = i + 1;
        while (j < s.size() && s[j] != '>') j++;

        if (j > s.size())
            return false;

        string sub = "";
        bool close = false;
        for (int k = i + 1; k < j; k++) {
            if (s[k] == '/') {
                close = true;
                if (k != i + 1)
                    return false;
            }
            else {
                sub += s[k];
            }
        }
        if (!sub.size())
            return false;

        if (close) {
            if (!top)
                return false;
            if (sub != st[top - 1])
                return false;
            top--;
        }
        else {
            st[top++] = sub;
        }

        i = j + 1;
    }
    if (!top)
        return true;
    return false;
}

int main() {
    freopen("xml.in", "r", stdin);
    freopen("xml.out", "w", stdout);

    cin >> s;
    for (int i = 0; i < s.size(); i++) {
        char mem = s[i];
        for (char j = 'a'; j <= 'z'; j++) {
            if (mem != j) {
                s[i] = j;
                if (check()) {
                    cout << s << endl;
                    return 0;
                }
            }
        }
        for (int j = 0; j < 3; j++) {
            if (mem != temp[j]) {
                s[i] = temp[j];
                if (check()) {
                    cout << s << endl;
                    return 0;
                }
            }
        }
        s[i] = mem;
    }

    return 0;
}