#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef tuple<ll, ll, ll> plll;
typedef vector<plll> vplll;
typedef pair<ll, ll> pll;
typedef vector<ll> vll;
typedef vector<pll> vpll;
typedef vector<vector<pll>> vvpll;
typedef vector<vector<ll>> vvll;
typedef vector<bool> vb;
typedef vector<vector<bool>> vvb;
#define loop(i, s, e) for (ll i = (s); i < (e); ++i)
#define loopr(i, e, s) for (ll i = (e)-1; i >= (s); --i)
#define all(a) a.begin(), a.end()
const ll inf = 1e9 + 7;
string s;
vector<string> vs;
void Init() {
}
void TypeLetter(char l) {
s+=l;
}
void UndoCommands(int u) {
loop(i,0,u) {
char c = s.back();
if (c=='D') {// this is undo
s.pop_back();
s+=vs.back();
vs.pop_back();
}
}
}
char GetLetter(int p) {
return s[p];
}
