#include #define ADD(a, b) a = (a + ll(b)) % mod #define MUL(a, b) a = (a * ll(b)) % mod #define MAX(a, b) a = max(a, b) #define MIN(a, b) a = min(a, b) #define rep(i, a, b) for(int i = int(a); i < int(b); i++) #define rer(i, a, b) for(int i = int(a) - 1; i >= int(b); i--) #define all(a) (a).begin(), (a).end() #define sz(v) (int)(v).size() #define pb push_back #define sec second #define fst first #define debug(fmt, ...) Debug(__LINE__, ":", fmt, ##__VA_ARGS__) using namespace std; typedef long long ll; typedef unsigned long long ull; typedef pair pi; typedef pair pl; typedef pair ppi; typedef vector vi; typedef vector vl; typedef vector mat; typedef complex comp; void Debug() {cout << '\n'; } templatevoid Debug(FIRST arg, REST... rest){ cout<ostream& operator<<(ostream& out,const vector& v) { out<<"[";if(!v.empty()){rep(i,0,sz(v)-1)out<ostream& operator<<(ostream& out,const pair& v){ out<<"("<> N; N--; cin >> P >> Q; p = P; q = Q; while(N--) { p = p + P * q * q / (1 - P * p); q = q * Q / (1 - P * p); } cout << p << "\n"; } int main() { #ifndef LOCAL ios::sync_with_stdio(false); cin.tie(0); #endif cout << fixed; cout.precision(20); srand((unsigned int)time(NULL)); #ifdef LOCAL //freopen("in.txt", "wt", stdout); //for tester freopen("in.txt", "rt", stdin); #endif solve(); #ifdef LOCAL cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n"; #endif return 0; }