how to use let python use negative numbers

how to use let python use negative numbers

I've been making a linear equation calculator and I'm wondering how to let python use negative numbers. Like int(), float() etc...
here is my code.
import time

print("Hello and welcome to the linear equation calculator.")

time.sleep(2)

print("Enter the first co-ordinate like this - (xx, yy): ")
coordnte1 = input()

print("Now enter the second co-ordinate like this, with the brackets, - (xx,yy): ")
coordnte2 = input()

print("Now the y-intercept: ")
yintrcpt = input()

ydif = coordnte2[1] - coordnte1[1]
xdif = coordnte2[0] - coodrnte1[0]
g = ydif / xdif

print("y = " + g + "x + " + yintrcpt)
And the problem:
Traceback (most recent call last):
  File "C:/Users/Dale/Documents/GitHub/new_python_rpi_experiments/linear.py", line 17,   in <module>
    ydif = coordnte2[1] - coordnte1[1]
TypeError: unsupported operand type(s) for -: 'str' and 'str'
Any help would be awesome!
(BTW I'm a total n00b at python. dont scream at me)