#include <bits/stdc++.h>
using namespace std;
#pragma GCC target("avx2")
#pragma GCC optimization("O3")
#pragma GCC optimization("unroll-loops")
long long modPow(long long a, long long b);
long long modInv(long long a);
void solve() {
  long long n, k;
  cin >> n >> k;
  string a, b;
  cin >> a;
  b = a;
  for (long long i = k; i < n; i++) {
    a[i] = a[i - k];
  }
  if (b > a) {
    long long itr = k - 1;
    while (a[itr] == '9') itr--;
    if (itr >= 0) {
      a[itr]++;
      for (long long it = itr + 1; it < k; it++) a[it] = '0';
    }
    for (long long i = k; i < n; i++) {
      a[i] = a[i - k];
    }
  }
  cout << n << "\n";
  for (long long i = 0; i < n; i++) cout << a[i];
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  solve();
}
long long modPow(long long a, long long b) {
  if (b == 0) return 1;
  if (b % 2 == 0) {
    long long x = a * a;
    x %= 1000000007;
    return modPow(x, b / 2);
  }
  return (a * modPow(a, b - 1)) % 1000000007;
}
long long modInv(long long a) { return modPow(a, 1000000007 - 2); }
