python please help I m getting max X not defined

Question

from sklearn.model_selection import cross_val_score

max_k = 100

cv_scores = [ ]

for k in range(1,max_K):

knn = KNeighborsClassifier(n_neighbors = K)

scores = cross_val_score(knn,X_train,y_train.values.ravel(),cv = 5,scoring = "accuracy")

cv_scores.append(scores.mean())

im getting max_k is not defined. how do I fix it