def find_min_trials(N):
    low = 1
    high = 2 * 10**5  # Sufficiently large upper bound given constraints

    while low < high:
        mid = (low + high) // 2
        current = mid * (mid + 1) // 2
        if current < N:
            low = mid + 1
        else:
            high = mid
    return low

N = int(input())
print(find_min_trials(N))