// #include <bits/allocator.h> // Temp fix for gcc13 global pragma
// #pragma GCC target("avx2,bmi2,popcnt,lzcnt")
// #pragma GCC optimize("O3,unroll-loops")
#include <bits/stdc++.h>
// #include <x86intrin.h>
using namespace std;
using namespace numbers;
#ifdef LOCAL
	#include "Debug.h"
#else
	#define debug_endl() 42
	#define debug(...) 42
	#define debug2(...) 42
	#define debug_bin(...) 42
#endif
// Returns the largest integer k with x >= k * y
template<class T, class U> U floor_div(T x, U y){
	assert(y > 0);
	return x / y - (x % y < 0);
}
// Returns the smallest integer k with x <= k * y
template<class T, class U> U ceil_div(T x, U y){
	assert(y > 0);
	return x / y + (x % y > 0);
}
template<class T> T &ctmin(T &x){ return x; }
template<class T, class Head, class ...Tail> T &ctmin(T &x, const Head &h, const Tail &... t){ return ctmin(x = min<T>(x, h), t...); }
template<class T> T &ctmax(T &x){ return x; }
template<class T, class Head, class ...Tail> T &ctmax(T &x, const Head &h, const Tail &... t){ return ctmax(x = max<T>(x, h), t...); }

// std::chunk_by cuz AtCoder is stuck on 3 years old gcc
vector<vector<int>> chunk_by(auto data, auto eq){
	vector<vector<int>> chunks;
	for(auto l = data.begin(); l != data.end(); ){
		auto r = next(l);
		vector<int> chunk{*l};
		while(r != data.end() && eq(*prev(r), *r)){
			chunk.push_back(*r);
			r = next(r);
		}
		chunks.push_back(chunk);
		l = r;
	}
	return chunks;
}



int main(){
	cin.tie(0)->sync_with_stdio(0);
	cin.exceptions(ios::badbit | ios::failbit);
	int n;
	long long k;
	string s;
	cin >> n >> k >> s, -- k;
	vector<long long> cnt(n + 1);
	cnt[n] = 1;
	for(auto i = n - 1; i >= 0; -- i){
		if(s[i] != '0'){
			cnt[i] += cnt[i + 1];
		}
		if(i + 2 <= n && (s[i] == '1' || s[i] == '2' && s[i + 1] <= '6')){
			cnt[i] += cnt[i + 2];
		}
		ctmin(cnt[i], numeric_limits<long long>::max() / 4);
	}
	assert(k < cnt[0]);
	string res;
	for(auto i = 0; i < n; ++ i){
		assert(s[i] != '0');
		if(k < cnt[i + 1]){
			res += char(s[i] - '1' + 'a');
		}
		else{
			assert(i + 2 <= n && (s[i] == '1' || s[i] == '2' && s[i + 1] <= '6'));
			k -= cnt[i + 1];
			assert(k < cnt[i + 2]);
			res += char(10 * (s[i] - '0') + s[i + 1] - '1' + 'a');
			++ i;
		}
	}
	cout << res << "\n";
	return 0;
}

/*

*/