疯狂的序列，其实是个等差数列求和(r*(r+1))/2 = n逆问题，输入n，求r

if __name__ == "__main__":
    n = int(sys.stdin.readline().strip())
    result = int((1+(1+8*n)**0.5)/2)
    if( (result**2 + result)/2 - result <= n <= (result**2 + result)/2):
        print(result)
    else:
        print(result+1)