#include <bits/stdc++.h>
using namespace std;
int n, k;
string s;
void povecaj() {
  int ind = k - 1;
  while (s[ind] == '9') {
    s[ind] = '0';
    ind--;
  }
  s[ind] = (char)((int)s[ind] + 1);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> k;
  cin >> s;
  bool p = 1;
  for (int i = 0; i < n - k; i++) {
    if (s[i] != s[i + k]) {
      p = 0;
      break;
    }
  }
  cout << n << '\n';
  if (p) {
    cout << s << '\n';
    return 0;
  }
  int ind = k;
  p = 0;
  for (int i = 0; i < n; i++) {
    if ((int)s[i] < (int)s[i % k]) {
      break;
    }
    if ((int)s[i] > (int)s[i % k]) {
      p = 1;
      break;
    }
  }
  if (p) {
    povecaj();
  }
  while (n > 0) {
    for (int i = 0; i < min(ind, n); i++) {
      cout << s[i];
    }
    n -= ind;
  }
  cout << '\n';
  return 0;
}
