Sum of Fibonacci sequence throws overflow error for large numbers - python-3.x

Question

For smaller numbers, till r = 1472 the below code is working well and good.
Code:
import math
def fib(n):
s5 = math.sqrt(5)
phi = (1 + s5) / 2;
return int(round(pow(phi, n) / s5));
def calculateSum(l, r):
# Using our deduced result
sum = fib(r + 2) - fib(l + 1)
res = sum % 1000000007
return res
l = 5
r =1400
print(calculateSum(l,r))
But when the r goes beyond 1473 it throws the following error.
Traceback (most recent call last):
File "C:/Users/HP/PycharmProjects/spoj/FIBOSUM.py", line 20, in <module>
print(calculateSum(l,r))
File "C:/Users/HP/PycharmProjects/spoj/FIBOSUM.py", line 14, in calculateSum
sum = fib(r + 2) - fib(l + 1)
File "C:/Users/HP/PycharmProjects/spoj/FIBOSUM.py", line 9, in fib
return int(round(pow(phi, n) / s5));
OverflowError: (34, 'Result too large')
Process finished with exit code 1
And I referred and searched about this error and found a way to mitigate using this link Error 34, Result too large. These changes are reflected below
Code2:
import decimal
def fib(n):
s5 = decimal.Decimal(5).sqrt()
phi = (1 + s5) / 2;
return int(round(pow(phi, n) / s5));
def calculateSum(l, r):
# Using our deduced result
sum = fib(r + 2) - fib(l + 1)
res = sum % 1000000007
return res
l = 5
r =4500000
print(calculateSum(l,r))
These changes are works for the numbers approximately less than say r = 4550000 but a number larger than 5000000 throws the following error
Traceback (most recent call last):
File "C:/Users/HP/PycharmProjects/spoj/FIBOSUM.py", line 20, in <module>
print(calculateSum(l,r))
File "C:/Users/HP/PycharmProjects/spoj/FIBOSUM.py", line 14, in calculateSum
sum = fib(r + 2) - fib(l + 1)
File "C:/Users/HP/PycharmProjects/spoj/FIBOSUM.py", line 9, in fib
return int(round(pow(phi, n) / s5));
decimal.Overflow: [<class 'decimal.Overflow'>]
Could anybody help me to resolve this problem?