All except one test case is passing. where is the logic flawed?
int overflowed
https://www.codechef.com/viewsolution/29886689
Tried with unsigned long long. Still the same test case is failing.
you need to change also these lines:
if(len%2 == 0)
result += (len/2)*(len+1);
else
result += len*((len+1)/2);
check this