#include <cstdio>
#include <cmath>

using namespace std;

double c, array [ 10 ], y, sum, tmp;
int n;

double bs ( double a, double b ) {
    c = ( a + b ) / 2;
    sum = 0;
    tmp = 1;
    for ( int i = 1; i <= n; ++i ) {
        tmp *= 1 + c;
        sum += array [ n - i ] * tmp;
    }
    if ( abs( b - a ) <= 0.00000001 ) return c;
    if ( sum > y ){ return bs ( a, c - 0.00001 ); } else { return bs ( c, b ); }
}

int main ( void ) {
    scanf ( "%d", &n );
    for ( int i = 0; i < n; ++i ) {
        scanf ( "%lf", &array [ i ] );
    }
    scanf ( "%lf", &y );
    printf ( "%.2lf\n", 100 * bs ( -1, 1 ) );
    return 0;
}