import math

def g(x):
    return x**2+3

def Integrate(f, a , b, n):
    h=(b-a)/n
    result=0
    for k in range(n):
        x=k*h+h/2
        result+=f(x)*h
    return result

F=input("f:")
A=float(input("a:"))
B=float(input("b:"))
N=int(input("n:"))
print(Integrate(F, A, B, N))

line 14, in Integrate
    result+=f(x)*h
TypeError: 'str' object is not callable