VI h[10001];
{
	ll res=ll_inf;
	ll@n,@m;
	ll md[2]{n,m};
	rep(i,n){
		ll@a;
		h[a].push_back(i);
	}
	rep(j,m){
		ll@b;
		for(int i:h[b]){
			ll val[2]{i,j};
			ll r=chineseRemainder(2,val,md);
			if(r>=0&&res>r+1){
				res=r+1;
			}
		}
	}
	wt(res==ll_inf?-1:res);
}