#include <bits/stdc++.h>
using namespace std;
long long n, m, c, p, q, r, y, k, a, b;
string s;
void input() {
  cin >> n >> k;
  cin >> s;
}
void solve() {
  cout << n << endl;
  vector<string> mat;
  long long flag = 1;
  for (long long i = 0; i < n - k; i++) {
    if (s[i] != s[i + k]) {
      flag = 0;
      break;
    }
  }
  if (flag == 1) {
    cout << s;
    return;
  }
  string temp = "";
  for (long long i = 0; i < k; i++) {
    temp += s[i];
  }
  mat.push_back(temp);
  long long j = k - 1;
  string res = mat[0];
  string fin2 = "";
  for (long long i = 0; i < n; i++) {
    fin2 += res[i % k];
  }
  if (fin2 >= s) {
    cout << fin2;
    return;
  }
  while (mat[0][j] == '9' && j >= 0) {
    j--;
  }
  if (j == -1) {
    res = mat[0];
  } else {
    mat[0][j]++;
    long long i = j + 1;
    for (; i < k; i++) {
      mat[0][i] = '0';
    }
    res = mat[0];
  }
  string fin = "";
  for (long long i = 0; i < n; i++) {
    fin += res[i % k];
  }
  cout << fin;
  return;
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long T = 1;
  while (T--) {
    input();
    solve();
  }
}
