#include<iostream>
#include<cstdlib>
#include<stack>
#include<fstream>

using namespace std;
int main()
{
    stack<int> st;
    int no,temp,last=1,x;
    bool startfound=false,possible=true;
    ifstream in("input.txt");
    if(!in) {
        cout<<"No such file"<<endl;
        exit(EXIT_SUCCESS);
    }

    in>>no;
    while(no){
        last=1;
        startfound=false;
        possible=true;
        while(!startfound){
            in>>temp;
            cout<<temp<<" "<<startfound;
            if(temp==1) {
                startfound=true;
            } else{
                st.push(temp);
            }
            no--;
            getchar();
        }
        cout<<"stack size:"<<st.size()<<endl;
        getchar();
        while(no--){
            in>>temp;
            if(temp-last != 1){
                x=st.top();
                if(x-last ==1) {
                    last=st.top();
                    st.pop();
                }else{
                    possible=false;
                    break;
                }
            }
            else
                last=temp;
        }
        while(st.size()>0 && possible == true ){
            if(st.top()-last == 1){
                last=st.top();
                st.pop();
            }else{
                possible=false;
            }
        }
        if(possible == false){
            while(no--) {
                in>>temp;
            }
            while(st.size() > 0)
                st.pop();
        }
    }
    in.close();
    possible?cout<<"true":cout<<"false";
    return 0;
}