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

ans = 10 ** 18
k, m, d = map(int, input().split())

for i in range(1, 10):
    if (calc(k, d, i) < m):
        ans = i - 1
        break

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)) :
        ans = min(i - d, ans)
        break
print(ans)