bibib

#include <fstream>
#include <cmath>
using namespace std;


int main()
{
    ifstream fin("input.txt");
    ofstream fout("output.txt");

    unsigned k, m, d, days = 0;
    fin >> k >> m >> d;

    long long books = m;

    double a = -4.9, b = k - 0.7, c = m * 0.2;
    double Di = b*b - 4*a*c;
    double x = -(b + sqrt(Di))/2/a;
    unsigned weeks = (unsigned) x;


    days = weeks * 7;
    books+= weeks * k*5;
    books-= (1 + days) * days/2;

    for (;;) {

        books-= days+1;
        if (d <= 5) books+= k;

        if (books >= 0) days++;
        else break;

        if (++d > 7) d = 1;
    }


    fout << days;
    return 0;
}