题目链接：https://www.codewars.com/kata/moves-in-squared-strings-i/train/objc
注意long long类型。
#import <Foundation/Foundation.h>
long long f(long long n, long long m) {
long long sum = 0;
long long q = n/m;
long long p = n%m;
sum+= (m*(m-1)/2)*q;
sum+= (p+1)*p/2;
return sum;
}
