#include <stdio.h>
#include <math.h>

#define size 21

double kDigitsRound(double c, int k){
    c = c * pow(10.0, k);
    c = floor(c + 0.5);
    c = c / pow(10.0, k);
    return c;
}

int main()
{
    int z[size], n, i, k=4;
    double c, a=0.0, b=1.0, fa=0.0, fb=0.0, fc=0.0;

    while(1){

      scanf("%d",&n);
        if(n==0){
        break;
        }
        else{
          for(i=0;i<n+1;i++){
            scanf("%d", &z[i]);

            fa=fa+(z[i]/(pow(1+a,i)));
            fb=fb+(z[i]/(pow(1+b,i)));
            }

      while(fa*fb<0){
        c=(a+b)/2;
        fc=fc+(z[i]/(pow(1+c,i)));

        if( fabs(fc) < 0.000001){
            break;
        }
        if( fa*fc > 0 ){
            a = c;
        }
        else { b = c; }
    }

    c=kDigitsRound(c, k);

    c=c*100;
    printf("%f%%\n",c);
       }
    }
    return 0;
}