#include <bits/stdc++.h>
using namespace std;
int t[27], cnt, n;
bool b[9], ans = 1;
char c[9], s[1005];
stack<bool> stk;
void dfs(int step)
{
    if (step == cnt + 1)
    {
        for (int i = 1; i <= n; ++i)
        {
            if ('a' <= s[i] && s[i] <= 'z') stk.push(b[t[s[i] - 'a' + 1]]);
            if (s[i] == '!')
            {
                int a = stk.top();
                stk.pop();
                stk.push(!a);
            }
            if (s[i] == '&')
            {
                int a = stk.top();
                stk.pop();
                int b = stk.top();
                stk.pop();
                stk.push(a & b);
            }
            if (s[i] == '|')
            {
                int a = stk.top();
                stk.pop();
                int b = stk.top();
                stk.pop();
                stk.push(a | b);
            }
            if (s[i] == '^')
            {
                int a = stk.top();
                stk.pop();
                int b = stk.top();
                stk.pop();
                stk.push(a ^ b);
            }
        }
        ans &= stk.top();
        stk.pop();
        return;
    }
    b[step] = 1;
    dfs(step + 1);
    b[step] = 0;
    dfs(step + 1);
}
int main()
{
    while (cin >> s[n + 1])
    {
        n++;
        if ('a' <= s[n] && s[n] <= 'z' && !t[s[n] - 'a' + 1]) c[++cnt] = s[n], t[s[n] - 'a' + 1] = cnt;
    }
    dfs(1);
    cout << (ans ? "YES" : "NO") << endl;
    return 0;
}