#include #include #include #include #include #include using namespace std; typedef long long int lont; int main() { lont A, B, C; cin >> A >> B >> C; A *= 60; C *= 3600; lont ans = 1; if (A <= B) { cout << -1 << endl; } else if(C/(A-B)%1){ cout << C / (A - B)+1 << endl; } else { cout << C / (A - B) << endl; } }