#include<bits/stdc++.h> using namespace std; int stk[105],top; int main(){ int n,op; cin>>n; while(n--){ cin>>op; if(op1){ int x; cin>>x; stk[++top]=x; } else top--; } if(op2&&top0){ cout<<"impossible!"; } else if(top0){ cout<<"impossible!"; }else{ cout<<stk[top]; } return 0; }

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