#include <bits/stdc++.h>
using namespace std;
inline int ci() {
  register char ch;
  int f = 1;
  while (!isdigit(ch = getchar())) f = ch == '-' ? -1 : 1;
  register int x = ch ^ '0';
  while (isdigit(ch = getchar())) x = (x * 10) + (ch ^ '0');
  return f * x;
}
enum { N = 200023 };
char s0[N];
char s1[N];
int main() {
  int n = ci(), k = ci();
  scanf("%s", s0 + 1);
  memcpy(s1, s0, sizeof(s0));
  for (register int i = (1); i <= (k); i++) {
    int t = i;
    while (t <= n) {
      s1[t] = s0[i];
      t += k;
    }
  }
  int fail = 0;
  for (register int i = (1); i <= (n); i++)
    if (s1[i] != s0[i]) {
      if (s1[i] < s0[i]) fail = 1;
      break;
    }
  if (fail) {
    for (register int i = (k); i >= (1); i--)
      if (s0[i] != '9') {
        s0[i]++;
        break;
      } else
        s0[i] = '0';
  }
  for (register int i = (1); i <= (k); i++) {
    int t = i;
    while (t <= n) {
      s1[t] = s0[i];
      t += k;
    }
  }
  printf("%d\n", n);
  puts(s1 + 1);
  return 0;
}
