#include #include #include using namespace std; using lint = long long; constexpr lint G = 6350400; // LCM(1,2,...,10)^2 void solve() { int n, k; cin >> n >> k; --k; if (k == 0) { cout << "0\n"; return; } vector xs(n); for (auto& x : xs) cin >> x; lint num = 0, dom = 0; for (int i = 1; i <= k; ++i) { num += G / xs[i] / xs[i - 1]; } for (int i = 1; i < n; ++i) { dom += G / xs[i] / xs[i - 1]; } { auto g = gcd(num, dom); num /= g, dom /= g; } cout << num << "/" << dom << "\n"; } int main() { cin.tie(nullptr); ios::sync_with_stdio(false); solve(); return 0; }