//interactive
ll@N,@M,x=0,y=0,R=1,S=1,c=0,b=1,T[2]{0,N-1};char@A[N][N];
REP(2N*N){if(A[y][x]>'.'&&b){b=0;while(c<2N*N)wt(2,1),c++;}if(c)wt(3,1);if(x==T[R]){R=!R;if(y==T[S]){S=!S;}wt(1,"UD"[S]);y+=2S-1;}else{wt(1,"LR"[R]);x+=2R-1;}}