#include <bits/stdc++.h>
using namespace std;
const long long maxn = 2e5 + 5;
inline long long read() {
  char c = getchar();
  long long t = 0, f = 1;
  while ((!isdigit(c)) && (c != EOF)) {
    if (c == '-') f = -1;
    c = getchar();
  }
  while ((isdigit(c)) && (c != EOF)) {
    t = (t << 3) + (t << 1) + (c ^ 48);
    c = getchar();
  }
  return t * f;
}
long long n, k, a[maxn], b[maxn];
char s[maxn];
signed main() {
  n = read(), k = read();
  scanf("%s", s + 1);
  for (long long i = 1; i <= n; i++) a[i] = s[i] - '0';
  for (long long i = 1; i <= k; i++) b[i] = a[i];
  for (long long i = k + 1; i <= n; i++) b[i] = b[i - k];
  long long flag = 1, pos = 0;
  for (long long i = k + 1; i <= n; i++) {
    if (b[i] > a[i]) {
      break;
    }
    if (b[i] < a[i]) {
      pos = i;
      flag = 0;
      break;
    }
  }
  printf("%d\n", n);
  if (!flag) {
    if (a[k] != 9) {
      for (long long i = k; i <= n; i = i + k) b[i]++;
    } else {
      for (long long i = k; i <= n; i = i + k) b[i] = 0;
      for (long long j = k - 1; j >= 1; j--) {
        if (a[j] != 9) {
          for (long long i = j; i <= n; i = i + k) b[i]++;
          break;
        } else {
          for (long long i = j; i <= n; i = i + k) b[i] = 0;
        }
      }
    }
    for (long long i = 1; i <= n; i++) printf("%d", b[i]);
    puts("");
    return 0;
  } else {
    for (long long i = 1; i <= n; i++) printf("%d", b[i]);
    puts("");
    return 0;
  }
  return 0;
}
