text: #include <bits/stdc++.h>
  
  using namespace std;
  
  int T, v[15];
  double lo, hi, mid;
  
  double solve(double IRR){
     double ans = v[0];
     for(int i = 1; i <= T; i++) ans += v[i] / pow(1 + IRR, i);
     return ans;
  }
  
  int main(){
     while(scanf("%d", &T), T){
        for(int i = 0; i <= T; i++) scanf("%d", &v[i]);
        lo = -0.99, hi = 10000.00;
        for(int it = 0; it < 80; it++){
           mid = (lo + hi) / 2.0;
           if(solve(mid) * solve(lo) > 0) lo = mid;
           else hi = mid;
        }
        printf("%.2lf\n", (lo + hi) / 2.0);
     }
     return(0);
  }
  