function sum_array(arr){
  var sum=0;
  for(var i=0 ; i<arr.length ; i++ ){
    sum += arr[i];
  }
  return sum;
}

function max_array(arr){
  var max_num=0;
  for(var max_index = 0 ; max_index<arr.length ; max_index++){
    max_num = Math.max(max_num, arr[max_index])
  }
  return max_num;
}

function main(input) {
  const inputs = input.split('\n');
  const counts = inputs[0].split(' ').map( x => parseInt(x, 10) );

  const n = counts[0];
  const k = counts[1];

  const input_numbers = inputs[1].split('').map( x => parseInt(x, 10) );
  const first_element = input_numbers[0];

if(n==1){
  console.log(1);
  return;
}

  var compressed_numbers = [];
  if(first_element==0){compressed_numbers=[0];}

  var pre_count = 1;
  var pre_number=input_numbers[0];

  pre_numbers = [input_numbers[0]];
  for(var  i=1 ; i<n ; i++){
    if(pre_number!=input_numbers[i]){
      compressed_numbers.push(pre_count);
      pre_count = 1;
      pre_number = input_numbers[i]
    }else{
      pre_count++;
    }
  }
  compressed_numbers.push(pre_count);

  var answer=0;
  var sub_array=[];
  const fetch_count = k*2+1;
  for(var  i=0 ; i<n ; i+=2){
    // k * 2 + 1 要素をとってくる
    num = (i+fetch_count)
    sub_array = compressed_numbers.slice(i, num)
    answer = Math.max(answer, sum_array(sub_array));
  }

  console.log(answer);
}

main(require('fs').readFileSync('/dev/stdin', 'utf8'));
