ll@H,@W,a=1,b=1;string@S[H],@T[H];rep(i,H)rep(j,W)a&=S[i][j]!=T[i][j],b&=S[i][j]!=T[H-i-1][W-j-1];double p=1;wt(a|b?sum[i,0,30]((i&1?b:a)?p/=1<<i:p)+1:-1);