#include<iostream>
#include<string>
#include<stack>
using namespace std;
stack<bool> stk;
string str[1000001];
int tot;
void operated(bool key){
	bool top1=stk.top();
	stk.pop();
	bool top2=stk.top();
	stk.pop();
	if(key){
		stk.push(top1&&top2);
	}else{
		stk.push(top1||top2);
	};
};
void answered(void){
	for(int iter=1;iter<=tot;++iter){
		if((str[iter]=="true"||str[iter]=="false")&&(str[iter-1]=="true"||str[iter-1]=="false")){
			cout<<"error";
			return;
		};
		if((str[iter]=="and"||str[iter]=="or")&&(str[iter=1]=="and"||str[iter-1]=="or")){
			cout<<"error";
			return;
		};
		if(str[iter]=="true"){
			stk.push(true);
		}else if(str[iter]=="false"){
			stk.push(false);
		};
		if(str[iter=1]=="and"){
			operated(true);
		};
	};
	while(stk.size()>1){
		operated(false);
	};
	if(stk.top()){
		cout<<"true";
	}else{
		cout<<"false";
	};
};
int main(void){
	bool temp=false;
	bool flag=false;
	while(cin>>str[++tot]){
		if(flag){
			if(str[tot]=="and"||str[tot]=="or"){
				cout<<"error";
				return 0;
			}else{
				flag=false;
			};
		};
		if(str[tot]=="not"){
			temp=!temp;
			flag=true;
			--tot;
		}else if(temp){
			if(str[tot]=="true"){
				str[tot]=="false";
			}else{
				str[tot]="true";
			};
			temp=false;
		};
	};
	if(str[1]=="and"||str[1]=="or"||str[tot]=="and"||str[tot]=="or"||str[tot]=="not"){
		cout<<"error";
		return 0;
	};
	answered();
	return 0;
};