#include <cstdio>
#include <cstdint>
#include <vector>
#include <set>
#include <map>
#include <string>

int main() {
  size_t N;
  intmax_t K;
  char buf[64];
  scanf("%zu %jd %s", &N, &K, buf);
  std::string S = buf;
  std::vector<intmax_t> atari(N);
  for (size_t i = 0; i < N; ++i)
    atari[i] = S[i]-'0';

  if (S == std::string(N, '0'))
    return !printf("%jd\n", K);

  std::vector<intmax_t> tada(N);
  for (size_t i = 0; i < N; ++i) {
    int cur = 1;
    tada[i] = 0;
    for (size_t j = i; cur && tada[i] <= intmax_t(N);) {
      ++tada[i];
      cur += atari[j] - 1;
      ++j %= N;
    }
  }

  intmax_t res = 0;
  std::map<intmax_t, intmax_t> seen;
  intmax_t last = 0;
  intmax_t ice = 0;
  while (true) {
    ++res;
    ice += tada[last];
    if (tada[last] > intmax_t(N))
      return !printf("%jd\n", res);
    if (ice >= K)
      return !printf("%jd\n", res);

    intmax_t next = (last + tada[last]) % N;
    seen.emplace(last, next);
    last = next;
    if (seen.count(last)) break;
  }

  intmax_t unit = 0;
  intmax_t period = 0;
  intmax_t cur = last;
  do {
    unit += tada[cur];
    ++period;
  } while (cur != last);

  res += (K - ice) / unit * period;
  ice += (K - ice) / unit * unit;

  while (ice < K) {
    ++res;
    ice += tada[last];
    last = (last + tada[last]) % N;
  }

  printf("%jd\n", res);
}