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

function max_array(arr){
  var max_num=0;
  for(max_index = 0 ; max_index<arr.length ; max_index++){
    if(arr[max_index] > max_num){
      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( 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);
  }

  sums=[];
  sub_array=[];
  for( i=0 ; i<n ; i++){
    if( i%2==0 ){
      if(first_element==0){
        // k * 2 -1 要素をとってくる
        sub_array = compressed_numbers.slice(i, i+k*2)
sums.push(sum_array(sub_array));
      } else {
        // k * 2 要素をとってくる
        sub_array = compressed_numbers.slice(i, i+k*2 + 1)
sums.push(sum_array(sub_array));
      }
    } else {
      if(first_element==0){
        // k * 2 要素をとってくる
        sub_array = compressed_numbers.slice(i, i+k*2+1)
sums.push(sum_array(sub_array));
      } else {
        // k * 2 -1 要素をとってくる
        sub_array = compressed_numbers.slice(i, i+k*2)
sums.push(sum_array(sub_array));
      }
    }
  }

  console.log(max_array(sums));
}

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