#include using namespace std; using ll=long long; const ll ILL=2167167167167167167; const int INF=2100000000; #define rep(i,a,b) for (int i=(int)(a);i<(int)(b);i++) #define all(p) p.begin(),p.end() template using _pq = priority_queue, greater>; template int LB(vector &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();} template int UB(vector &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();} template bool chmin(T &a,T b){if(b bool chmax(T &a,T b){if(a void So(vector &v) {sort(v.begin(),v.end());} template void Sore(vector &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});} bool yneos(bool a,bool upp=false){if(a){cout<<(upp?"YES\n":"Yes\n");}else{cout<<(upp?"NO\n":"No\n");}return a;} template void vec_out(vector &p,int ty=0){ if(ty==2){cout<<'{';for(int i=0;i<(int)p.size();i++){if(i){cout<<",";}cout<<'"'< T vec_min(vector &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmin(ans,x);return ans;} template T vec_max(vector &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmax(ans,x);return ans;} template T vec_sum(vector &a){T ans=T(0);for(auto &x:a) ans+=x;return ans;} int pop_count(long long a){int res=0;while(a){res+=(a&1),a>>=1;}return res;} template T square(T a){return a * a;} void solve(); // POP'N ROLL MUSIC / TOMOO int main() { ios::sync_with_stdio(false); cin.tie(nullptr); int t = 1; // cin >> t; rep(i, 0, t) solve(); } void solve(){ ll N, K; cin >> N >> K; string S; cin >> S; vector dp(N + 1); dp[N] = 1; for (int i = N - 1; i >= 0; i--){ if (S[i] != '0'){ dp[i] += dp[i + 1]; if (i + 1 != N && stoi(S.substr(i, 2)) <= 26){ dp[i] += dp[i + 2]; } } chmin(dp[i], K + 1); } string ans; int ind = 0; K--; while (ind != N){ assert(S[ind] != '0'); if (dp[ind + 1] <= K){ K -= dp[ind + 1]; ans += (char)('a' + stoi(S.substr(ind, 2)) - 1); ind += 2; } else{ ans += (char)('a' + S[ind] - '1'); ind++; } } cout << ans << "\n"; }