<?php
    $input = preg_split('/ /',fgets(STDIN));
    $leaves = $input[0];
    $fall_number = $input[1];
    $start_month = $input[2];
    $wind_period = $input[3];
    $end_month = $start_month + $wind_period - 1;
    $count = 0;
    $this_month = 1;

    while($leaves > 0){
        $count += 1;
        if($start_month <= $this_month && $this_month <= $end_month){
            $leaves -= $fall_number*2;
        }else{
            $leaves -= $fall_number;
        }
        if($this_month == 12){
            $this_month = 1;
        }else{
            $this_month++; 
        }
    }
    print $count . "\n";
?>