#pragma GCC optimize("Ofast")
#pragma GCC target("avx2")

char*mmap();

#define rd(v) long v=0;{long _c;while(_c=*rp++-48,_c>=0)v=v*10+_c;}
#define rep(v,e) for(long v=0;v<e;++v)

int l[200000];

main(){
	char*rp=mmap(0l,1l<<25,1,2,0,0ll);
	rd(n);
	rep(i,n){
		rd(li);
		l[i]=li;
	}
	rd(k);
	double z=0;
	for(double d=d=5e8;d>=z*5e-10;d*=.5){
		double t=z+d;
		double v=1/t;
		long c=0;
		rep(i,n){
			c+=(long)(l[i]*v);
		}
		if(c>=k){
			z=t;
		}
	}
	printf("%.10f\n",z);
}