ll@n,@e;
assert(e); //// test
vector<ll>h;
h.push_back(0);
long k=1;
rep(i,e){
	vector<ll>g;
	for(ll v:h){
		rep(j,5){
			ll w=v+j*k;
			if((w*w-n)%(k*5)==0){
				g.push_back(w);
			}
		}
	}
	h=g;
	k*=5;
}
if(h.empty()){
	wt("NaN");
}else{
	wt(h[0]);
}