#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize(2)
typedef long long LL;
char op[1005],s[1005],x[5];
int pos=0,oppos=0,numpos=0,idx=0,bianhao[305];
bool num[1005];
bool check(int val){
    oppos=numpos=0;
    bool a,b;
    for (int i=1;i<=pos;++i){
        if ((s[i]>='a')&&(s[i]<='z')){num[++pos]=((val>>(bianhao[(int)s[i]]-1))&1);}
        if (s[i]=='&'){
            b=num[pos--];
            a=num[pos--];
            num[++pos]=a&b;
        }
        if (s[i]=='|'){
            b=num[pos--];
            a=num[pos--];
            num[++pos]=a|b;
        }
        if (s[i]=='^'){
            b=num[pos--];
            a=num[pos--];
            num[++pos]=a^b;
        }
        if (s[i]=='!'){num[pos]=!num[pos];}
    }
    return num[pos];
}
int main(){
    while (~scanf("%s",x+1)){s[++pos]=x[1];if ((x[1]>='a')&&(x[1]<='z')){if (!bianhao[(int)(x[1])]){bianhao[(int)(x[1])]=++idx;}}}
    for (int i=0;i<(1LL<<idx);++i){
        if (!check(i)){return puts("NO"),0;}
    }
    puts("YES");
    return 0;
}