#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using PII = pair<int, int>;
using PIL = pair<int, ll>;
template <typename A, typename B>
string to_string(pair<A, B> p);
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);
string to_string(const string& s) { return '"' + s + '"'; }
string to_string(const char* s) { return to_string((string)s); }
string to_string(bool b) { return (b ? "true" : "false"); }
string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}
template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}
template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto& first : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(first);
  }
  res += "}";
  return res;
}
template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ")";
}
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}
int bs_biggest(int l, int r, function<bool(int)> check) {
  assert(l <= r);
  while (l < r) {
    int mid = (l + r + 1) / 2;
    if (check(mid))
      l = mid;
    else
      r = mid - 1;
  }
  return l;
}
int bs_smallest(int l, int r, function<bool(int)> check) {
  assert(l <= r);
  while (l < r) {
    int mid = (l + r) / 2;
    if (check(mid))
      r = mid;
    else
      l = mid + 1;
  }
  return l;
}
ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
void my_main() {
  int n, k;
  cin >> n >> k;
  string s;
  cin >> s;
  auto val = vector<int>(n + 1);
  for (int i = (1), i_end_ = (n + 1); i < i_end_; ++i) val[i] = s[i - 1] - '0';
  auto ans = vector<int>(n + 1);
  for (int i = (1), i_end_ = (k + 1); i < i_end_; ++i) ans[i] = val[i];
  for (int i = (k + 1), i_end_ = (n + 1); i < i_end_; ++i) ans[i] = ans[i - k];
  auto cmp = [&](const vector<int>& v1, const vector<int>& v2) -> bool {
    for (int i = (1), i_end_ = (n + 1); i < i_end_; ++i) {
      if (v1[i] < v2[i]) return true;
      if (v1[i] > v2[i]) return false;
    }
    return false;
  };
  if (!cmp(ans, val)) {
  } else {
    int cur = k;
    while (cur >= 1) {
      ++ans[cur];
      if (ans[cur] == 10) {
        ans[cur] -= 10;
        --cur;
      } else {
        break;
      }
    }
    assert(ans[1] < 10);
    for (int i = (k + 1), i_end_ = (n + 1); i < i_end_; ++i)
      ans[i] = ans[i - k];
  }
  cout << n << endl;
  for (int i = (1), i_end_ = (n + 1); i < i_end_; ++i) cout << ans[i];
  cout << endl;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout << fixed << setprecision(12);
  my_main();
  return 0;
}
