Python code

Implement a simple text editor. The editor initially contains an empty string, S$.$

Perform Q operations of the following $4$ types:

append$($W$)-$ Append string W to the end of S$.$

delete$($k$)-$ Delete the last k characters of S$.$

print$($k$)-$ Print the kth character of S$.$

undo$()-$ Undo the last $($not previously undone$)$ operation of type $1$ or $2,$ reverting S to the state it was in prior to that operation.

Example

S$=$ 'abcde'

ops$=[\text{'}1$ fg$\text{'},\text{'}36\text{'},\text{'}25\text{'},\text{'}4\text{'},\text{'}37\text{'},\text{'}4\text{'},\text{'}34\text{'}]$

operation

index S ops$[$index$]$ explanation

$--------------------------------$

$0$ abcde $1$ fg append fg

$1$ abcdefg $36$ print the $6$th letter $-$ f

$2$ abcdefg $25$ delete the last $5$ letters

$3$ ab $4$ undo the last operation, index $2$

$4$ abcdefg $37$ print the $7$th characgter $-$ g

$5$ abcdefg $4$ undo the last operation, index $0$

$6$ abcde $34$ print the $4$th character $-$ d

The results should be printed as:

f

g

d

Input Format

The first line contains an integer, Q$,$ denoting the number of operations.

Each line i of the Q subsequent lines $($where $0<=$i