#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long int n, k;
  cin >> n >> k;
  string num, temp;
  cin >> num;
  temp = num;
  long long int len = num.length();
  map<long long int, int> mp;
  for (int i = 0; i <= n - 1; i++) mp[i] = 1;
  int flag = 0;
  long long int lazy = 0;
  for (long long int i = 0; i < len; i++) {
    if (mp[i] == 1) {
      lazy = i;
      for (long long int j = i + k; j < len; j += k) {
        num[j] = num[i];
        mp[j] = 0;
      }
    } else if (flag == 0) {
      long long int diff = (num[i] - '0') - (temp[i] - '0');
      if (diff > 0) {
        flag = 1;
        continue;
      } else if (diff == 0) {
        continue;
      } else if (diff < 0) {
        int fg = 0;
        for (long long int q = lazy; q < num.length(); q += k) {
          if (num[q] == '9') {
            if (fg == 0) {
              num += '9';
              fg = 1;
            }
            num[q] = '0';
            for (int b = q - 1; b >= q - k + 1; b--) {
              if (num[b] == '9')
                num[b] = '0';
              else {
                num[b] = ((num[b] - '0') + 1) + '0';
                break;
              }
            }
          } else {
            num[q] = ((temp[lazy] - '0') + 1) + '0';
          }
        }
        flag = 1;
      }
    }
  }
  num[len - 1] = num[len - 1 - k];
  if (num.length() > len)
    cout << len << endl << num.substr(0, len) << endl;
  else
    cout << len << endl << num << endl;
  return 0;
}
