#include <bits/stdc++.h>
using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
void c_p_c() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
}
void solve() {
  long long n, k;
  cin >> n >> k;
  long long ar[n];
  cout << n << endl;
  for (long long i = 0; i < n; i++) {
    char c;
    cin >> c;
    ar[i] = c - '0';
  }
  long long f = 1;
  for (long long i = 0; i < n - k; i++) {
    if (ar[i] > ar[i + k]) {
      f = 1;
      break;
    }
    if (ar[i] < ar[i + k]) {
      f = 0;
      break;
    }
    ar[i + k] = ar[i];
  }
  if (f == 0) {
    long long j = 1;
    while (ar[k - j] == 9) {
      ar[k - j] = 0;
      j++;
    }
    ar[k - j]++;
    for (long long i = 0; i < n; i++) {
      cout << ar[i % k];
    }
  } else {
    for (long long i = 0; i < n; i++) {
      cout << ar[i % k];
    }
  }
}
int32_t main() {
  clock_t z = clock();
  c_p_c();
  {
    solve();
    cout << endl;
  }
  cerr << "Total Time : " << ((double)(clock() - z) / CLOCKS_PER_SEC);
  return 0;
}
