module mux_64x1 (in,sel,out);
input [63:0] in;
input [5:0]sel;
output out;
wire out0_w, out1_w;

mux_32x1 m64_0(.in(in[31:0]),.sel(sel[4:0]),.out(out0_w));
mux_32x1 m64_1(.in(in[63:32]),.sel(sel[4:0]),.out(out1_w));
mux_2x1 m64_2(.a(out0_w),.b(out1_w),.sel(sel[5]),.out(out));

endmodule