Need help with Python code for best performance

$1.$ CountBananas Calculate how many times you can print the word "BANANA" using the letters given in string S$.$

Task description

A string S made of uppercase English letters is given. In one move,six letters forming the word "BANANA" $($one $\text{'}$B$\text{'},$ three $\text{'}$A$\text{'}$s and two $\text{'}$N$\text{'}$s$)$ can be deleted from S$.$ What is the maximum number times such a move can be applied to S$?$

Write a function:

function solution$($S: string$)$: number;

that, given a string S of length N$,$ returns the maximum number of moves that can be applied.

Examples:

$1.$ Given S $=$ "NAABXXAN", the function should return $1.$

NAABXXAN

$2.$ Given S $=$ "NAANAAXNABABYNNBZ", the function should return $2.$

NAANAAXNABABYNNBZ

NAAXNABYNBZ

XBYNZ

$3.$ Given S $=$ "QABAAAWOBL", the function should return $0.$

QABAAAWOBL

Write an efficient algorithm for the following assumptions$*$

$.$ N is an integer within the range $[1.\mathrm{.}100,000)$; string S is made only of uppercase letters $($A$-$Z$).$