1.
n=input("n=")
n=int(n)
sum=0
if n<0:
    print "Bang bang"
else:
    for x in xrange(1,n+1):
        sum+=x*x
    print "sum= ",sum


2.
n=input("n= ")
n=int(n)
sum=0
if n>=0:
    for x in xrange(0,n+1):
        if x%2==0:
            sum+=x
    print "sum",sum
if n<0:
    for x in xrange(0,abs(n)+1):
        if x%2!=0:
            sum-=x
    print "sum= ",sum


3.
while 1:
    n=input("n= ")
    n=int(n)
    sum=0
    if n<0:
        break
    else:
        if n<0:
            print "Bang bang"
        else:
            for x in xrange(1,n+1):
                sum+=x*x
            print "sum",sum