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#include<stdio.h>
#include<math.h>
double a[120];
double f(int n,double m) {
    double sum=0;
    for(int i=0; i<=n; i++) {
        sum+=(double)pow(m,(double)(i+1))*a[i]/(i+1);
    }
    return sum;
}
int main() {
    int n;
    while(scanf("%d",&n),n) {
        for(int i=n; i>=0; i--)
            scanf("%lf",&a[i]);
        double s,e;
        scanf("%lf %lf",&s,&e);
        printf("%.3lf\n",(f(n,e)-f(n,s))/(e-s));
    }
    return 0;
}