#include <bits/stdc++.h>
#pragma GCC optimize(2)
using namespace std;
#define int long long
//fixed << setprecision()
int n;
int lnum;

string cs;
string s;
map<char, bool> is_ex;
map<char, bool> v;

stack<bool> stk;

bool check()
{
	//cout << "*start*" << endl;
	for(int i = 0;i < s.size();i++)
	{
		
		if('a' <= s[i] && s[i] <= 'z')
		{
			stk.push(v[s[i]]);
		}
		else
		{
			bool u = stk.top();stk.pop();
			if(s[i] == '!')
			{
				stk.push((!u));
				continue;
			}
			
			bool v = stk.top();stk.pop();
			if(s[i] == '&')
			{
				stk.push((u & v));
			}
			else if(s[i] == '|')
			{
				stk.push((u | v));
			}
			else if(s[i] == '^')
			{
				stk.push((u ^ v));
			}
			
		}
	}
	//cout << "*end*" << endl;
	return stk.top();
}

void dfs(int pos)
{
	if(pos == lnum)
	{
		/*
		for(int i = 0;i < lnum;i++)
		{
			cout << v['a' + i] << " ";
		}
		cout << endl;
		*/
		bool p = check();
		if(!p)
		{
			cout << "NO" << endl;
			exit(0);
		}
		stk.pop();
		return;
	}
	v[('a' + pos)] = 0;
	dfs(pos + 1);
	v[('a' + pos)] = 1;
	dfs(pos + 1);
}
signed main()
{
	ios::sync_with_stdio(false);
	getline(cin, cs);
	for(int i = 0;i < cs.size();i++)
	{
		if('a' <= cs[i] && cs[i] <= 'z')
		{
			is_ex[cs[i]] = true;
		}
		if(cs[i] != ' ')
			s += cs[i];
	}
	lnum = is_ex.size();
	/*
	for(int i = 0;i < lnum;i++)
	{
		cout << (char)(i + 'a') << " \n"[i == lnum - 1];
	}
	*/
	dfs(0);
	cout << "YES" << endl;
	return 0;
}