#include <bits/stdc++.h>

#define FOR(i, a, b) for(auto i=a; i<=b; ++i)
#define REP(i, a, b) for(auto i=a; i<b; ++i)
#define FORI(i, a, b) for(auto i=a; i!=b+1-2*(a>b); i+=1-2*(a>b))
#define REPI(i, a, b) for(auto i=a-(a>b); i!=b-(a>b); i+=1-2*(a>b))

using namespace std;


class BearPasswordAny
{
public:
    string findPassword(vector<int> val)
    {
        string result = "";
        int N = val.size(), calc;
        char ch = 'a';

        for(int i=N-1; i>=0; --i)
        {
            calc = find_occur(result, i+1);

//            cout<<val[i]<<" "<<calc<<endl;

            if(calc > val[i])
                return "";

            while(val[i] - calc)
            {
                FOR(j, 0, i)
                    result += ch;

                ch = 'b' - ch + 'a';
                ++calc;
            }

//            cout<<result<<endl;
        }

        if(result.size() != N)
            return "";

        return result;
    }


    int find_occur(string &str, int num)
    {
        int cnt = 1, ret = 0;

        if(!str.empty()  &&  cnt >= num)
            ++ret;

        REP(i, 1, str.size())
        {
            if(str[i] == str[i-1])
                ++cnt;
            else
                cnt = 1;

            if(cnt >= num)
                ++ret;
        }

        return ret;
    }
};