def calc(k, d, i) :
    res = ( (i - d + 1) * ((i - d + 1) + 1) )// 2
    for j in range(d, 7):
        if (j <= 5) :
            res -= k
    while (i % 7 != 0) :
        if (i % 7 <= 5) :
            res -= k
        i -= 1
    res -= (((i - 7) // 7) * 5) * k
    return res

k, m, d = map(int, input().split())

flag = False

cnt = m
for i in range(1, 1488):
    cnt -= i
    if ((i + d - 2) % 7 < 5):
        cnt += k
    if (cnt < 0):
        flag = True
    if (flag):
        print(i - 1)

if (not flag):
    ll = 1
    rr = 7 * 10 ** 10
    while (rr - ll > 1) :
        mm =(ll + rr)// 2
        if (m >= calc(k, d, 7 * mm)):
            ll = mm
        else:
            rr = mm
    for i in range(max(d, 7 * (rr) - 100), max(d, 7 * rr + 100)):
        if (m < calc(k, d, i)) :
            print(i - d)
            break