import sys
input = lambda : sys.stdin.readline().rstrip()

sys.setrecursionlimit(2*10**5+10)
write = lambda x: sys.stdout.write(x+"\n")
debug = lambda x: sys.stderr.write(x+"\n")

n = int(input())
v = 0
for i in range(1, 10**6):
    if v+i>=n:
        break
    v += i
ans = i
print(ans)