#define _USE_MATH_DEFINES #define _CRT_SECURE_NO_WARNINGS #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; //#include int main() { long long int a, b, c; cin >> a >> b >> c; a *= 60; c *= 3600; //cout << c; //cout << a << " " << c << endl;; long long int r = c/(a-b); if (c%a)r++; if (a <= b)cout << -1 << endl; else cout << r++ << endl; return 0; }