F

#include <iostream>
#include <string>
#include <vector>

using namespace std;

int k;

bool srvn(string s1, string s2) {
    vector<int> srv(k, 0);

    for (int i = 0; i < s1.length(); i++) {
        srv[s1[i] - 'a']++;
        srv[s2[i] - 'a']--;
    }

    for (int i : srv) {
        if (i != 0)
            return false;
    }

    return true;
}

int main() {
    string s1, s2, pods1, pods2;
    int n;
    char a, b;
    cin >> k >> n;

    vector<vector<bool>> vec(k, vector<bool>(k, false));
    for (int i = 0; i < n; i++) {
        cin >> a >> b;
        vec[a - 'a'][b - 'a'] = true;
        vec[b - 'a'][a - 'a'] = true;
    }

    cin >> s1 >> s2;

    if (!srvn(s1, s2)) {
        cout << "NO";
        return 0;
    }

    for (int i = 1; i < k; i++) {
        for (int j = 0; j < i; j++) {
            if (vec[i][j]) {
                pods1 = "";
                pods2 = "";

                char a = i + 'a';
                char b = j + 'a';


                for (int k = 0; k < s1.size(); k++) {
                    if (s1[k] == a || s1[k] == b) pods1 += s1[k];
                    if (s2[k] == a || s2[k] == b) pods2 += s2[k];
                }
                if (pods1 != pods2) {
                    cout << "NO";
                    return 0;
                }
            }
        }
    }

    cout << "YES";
    return 0;
}