#include <bits/stdc++.h>
using namespace std;
int n, k;
int a[300005], b[300005];
int main() {
  int tests = 1;
  while (tests--) {
    scanf("%d%d", &n, &k), printf("%d\n", n);
    for (int i = 1; i <= (n); ++i) scanf("%1d", a + i);
    for (int i = 1; i <= (n); ++i) b[i] = a[(i - 1) % k + 1];
    int ok = 0;
    for (int i = 1; i <= (n); ++i)
      if (b[i] != a[i]) {
        if (b[i] < a[i]) ok = 1;
        break;
      }
    if (ok) ++b[k];
    for (int i = k; i >= (1); --i)
      if (b[i] == 10)
        b[i] = 0, ++b[i - 1];
      else
        break;
    for (int i = 1; i <= (n); ++i) printf("%d", b[(i - 1) % k + 1]);
  }
  return 0;
}
