k = int(input())
s = 0
for i in range(k//2, 0, -1):
    if i*(1+i)//2 <= k:
         t = k-(i*(1+i)//2)
         for j in range(1, i+1):
             s += pow(j, 2)
         s += t*(i+1)
         break
    else:
        continue
print(s, end='')