# 给的k不在3 6 10 15这类刚好等于sum+=i*i的数字而是在这些数字之间的数,用超出部分(k - count) * i,然后加上在 3 6 10 15这类数中符合规律的sum+=i*i
def main():
    k=int(input())
    sum,count,n,temp,ls=0,0,3,3,[]
    def f():
        while True:
            temp+=n
            n+=1
            if temp>1000:
                break    
            yield temp
    for t in f():
        ls.append(t)
    for i in range(len(ls)-1):
        if ls[i]<k<ls[i+1]:
            sum+=i*i
            k-=count
            if k<0:
                break
        else:
            ex=(k-ls[i])*i
    print(sum+ex)
if __name__=="__main__":
    main()