#include <bits/stdc++.h>
using namespace std;
int main() {
  int t = 1;
  while (t--) {
    long long int n, k;
    cin >> n >> k;
    string s;
    cin >> s;
    string s1 = "";
    s1 += s.substr(0, k);
    int ii = n / k;
    if ((n % k) != 0) {
      ii++;
    }
    string help = s1;
    for (int i = 0; i < ii - 1; i++) {
      help += s1;
    }
    help = help.substr(0, n);
    if (help >= s) {
      cout << n << endl;
      cout << help << endl;
      continue;
    } else {
      cout << n << endl;
      int index = k - 1;
      while (index >= 0 && help[index] == '9') {
        help[index] = '0';
        index--;
      }
      string s2 = "";
      s2 += (help.substr(0, k));
      string append = help.substr(0, k);
      for (int i = 0; i < ii - 1; i++) {
        s2 += append;
      }
      s2 = s2.substr(0, n);
      char ch = s2[index];
      char replaces = ch + 1;
      s2[index] = replaces;
      while (index + k < n) {
        index += k;
        s2[index] = replaces;
      }
      cout << s2 << endl;
    }
  }
  return 0;
}
