#include <bits/stdc++.h>

using namespace std;

long long calc(long long k, long long d, long long i)
{
    long long res = (i - d + 1) * ((i - d + 1) + 1) / 2;

    for (int j = d; j <= 7; j++)
        res -= ((j <= 5) ? k : 0);

    for (; i % 7 != 0; i--)
        res -= (((i % 7) <= 5) ? k : 0);

    res -= ((i - 7) / 7) * 5 * k;

    return res;
}

int main()
{
    long long k, m, d;
    cin >> k >> m >> d;

    long long ll, mm, rr;
    ll = 0, rr = 1e8;

    while (rr - ll > 1)
    {
        mm = (ll + rr) / 2;
        (m >= calc(k, d, 7 * mm) ? ll : rr) = mm;
    }

    for (int i = max(d, 7 * (rr - 1)); i <= 7 * rr; i++)
    {
        if (m < calc(k, d, i))
        {
            cout << (i - d);
            return 0;
        }
    }

    return 0;
}