#include <bits/stdc++.h>
using namespace std;
const long long N = 1e5 + 5;
int32_t main() {
  ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
  long long t = 1;
  while (t--) {
    long long n, k;
    cin >> n >> k;
    string s, temp;
    ;
    cin >> s;
    s = '@' + s;
    temp = s;
    bool flag = true;
    for (long long i = 1; i <= k; i++) {
      for (long long j = i + k; j <= n; j += k) {
        if (s[j] != s[i]) {
          flag = false;
        }
      }
    }
    if (!flag) {
      for (long long i = 1; i <= k; i++) {
        for (long long j = i + k; j <= n; j += k) {
          s[j] = s[i];
        }
      }
      for (long long i = 1; i <= n; i++) {
        if (s[i] > temp[i]) break;
        if (s[i] < temp[i]) {
          for (long long j = k; j >= 1; j--) {
            if (s[j] != '9') {
              s[j]++;
              break;
            } else if (s[j] == '9') {
              s[j] = '0';
            }
          }
          break;
        }
      }
      for (long long i = 1; i <= k; i++) {
        for (long long j = i + k; j <= n; j += k) {
          s[j] = s[i];
        }
      }
    }
    cout << n << "\n";
    for (long long i = 1; i <= n; i++) cout << s[i];
  }
  return 0;
}
