Error with if statement and multiple conditions

I'm having a problem with if statement that's checking if input is correct. It when I input M or F it prints out "Wrong input" and I don't understand it very clearly.

def check(aw,iw):
    if abs(aw-iw)<5 :
        print "Your weight is normal."
    elif abs(aw-iw)>5 and abs(aw-iw)<15 :
        print "Your weight is about normal."
    else:
        print "Your weight is not normal."
    return

print "Enter your gender (M/F)"
gender=raw_input()
gender=int(gender)
if gender!='M' or gender!='F':
    print "Wrong input."
else:
    if gender=='M':
        w=raw_input("Enter your weight (kg) :")
        h=raw_input("Enter your height (cm) :")
        idw=110-h
        check(w,idw)
    else:
        w = raw_input("Enter your weight (kg) :")
        h = raw_input("Enter your height (cm) :")
        idw = 110 - h
        check(w, idw)