#include <bits/stdc++.h>   using namespace std;   int n, l[605], r[605];   string str, tmp;   stack<string> S;   int main() {     cin >> n;     for (int i = 0; i < n; i++) cin >> l[i] >> r[i];     for (int i = n - 1; i >= 0; i--) {       if (l[i] == 1) {         S.push( () );         continue;       } else {         int lenth = 1;         tmp =   ;         while (!S.empty() && lenth < l[i]) {           tmp = tmp + S.top();           lenth += S.top().length();           S.pop();         }         tmp =  (  + tmp +  ) ;         S.push(tmp);         if (lenth > r[i] || lenth < l[i]) {           cout <<  IMPOSSIBLE  << endl;           return 0;         }       }     }     while (!S.empty()) {       cout << S.top();       S.pop();     }     return 0;   }   