#洛谷P8749 [蓝桥杯 2021 省 B] 杨辉三角形
n = int(input())
yh = []
i = 0
for i in range(1000):
    yh.append([1] + [0] * 1000)
for i in range(1,1000):
    for j in range(1,1001):
        yh[i][j] = yh[i-1][j] + yh[i-1][j-1]
        if yh[i][j] == 0:
            break
    if n in yh[i]:
        x = i
        y = j
        break
ans = 0
num = []
for i in range(x + 1):
    for j in range(x + 1):
        if yh[i][j] != 0:
            num.append(str(yh[i][j]))
        if yh[i][j] == 0:
            break
ans = num.index(str(n)) + 1
print(ans)

20分，谁能救救我！