LaTeX matrices creator

#!/bin/python3

# --- Constants ---
mtypes = ['b','v','p', '']

# --- Code ----

while True:
    print("Select matrix type:\n1. bmatrix\t2. vmatrix\t3. pmatrix\t4. matrix\n")
    stype = input('> ')

    try:
        stype = int(stype)
        if stype > 4 or stype < 1:
            print("Please input a number from 1 to 4\n")
            continue
    except:
        print("Please input a number from 1 to 4\n")
        continue
    break

stype = mtypes[stype - 1]

while True:
    print ("\nInput the amount of matrix lines")

    try:
        lines = int(input('> '))
        if lines < 1:
            print("Please input a positive number\n")
            continue
    except:
        print("Please input a positive number\n")
        continue
    break

while True:
    print ("\nInput the amount of matrix columns")

    try:
        columns = int(input('> '))
        if columns < 1:
            print("Please input a positive number\n")
            continue
    except:
        print("Please input a positive number\n")
        continue
    break

latex = "\\begin{" + stype + "matrix} "

print("Iteration started. Input the correspondent LaTeX of the elements for each line:")
for i in range(0, lines):
    print("Line " + str(i+1) + ":")
    for j in range(0, columns):
        print("\tElement " + str(j+1) + ": ", end="")
        element = input()
        latex += element
        if j != columns-1:
            latex += " & "
        print("\n")

    if i != lines-1:
        latex += " \\\\ "
    print("\n\n")

latex += " \\end{" + stype + "matrix}"

print("Process ended. LaTeX: " + latex)
input()