module person_counter(LEDR, KEY, CLOCK_50);
    input CLOCK_50; // 50 MHz clock generator
    input [3:0] KEY; // use the "0"-th button as a reset button
    output [17:0] LEDR;
    wire reset;
    wire button;

    assign reset = !KEY[0];
    assign button = !KEY[1];
    count_seconds u1(LEDR, reset, button, CLOCK_50);
endmodule

module count_seconds(red_led, reset, button, clock);
    input clock;
    input button;
    input reset;
    output [17:0] red_led;
    reg [30:0] counter;
    reg led;
    reg [18:0] seconds_counter; // counts seconds

    assign red_led = seconds_counter[18:1]; // select "seconds"

always @(posedge clock or posedge button or posedge reset)
    if (reset) begin
        counter = 0;
        led = 0;
    end

// process for counting seconds
always @(posedge clock or posedge reset)
    if (reset)
        seconds_counter = 0;
    else
        if (button)
            seconds_counter = seconds_counter + 1;
endmodule