import math

N = int(input())
left = 1
right = 2 * 10**6  # Upper bound for binary search

# Binary search to find the smallest m where m(m+1)/2 > N
while left < right:
    mid = (left + right) // 2
    if mid * (mid + 1) // 2 > N:
        right = mid
    else:
        left = mid + 1

m = left
print(N - m)