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;
}

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

  if(first_element==0){compressed_numbers.unshift(0);}

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