import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }




void main() {
  try {
    for (; ; ) {
      const N = readInt();
      const K = readLong();
      auto S = readToken().map!(c => (c - '0')).array;
      
      auto SSum = new int[N + 1];
      foreach (i; 0 .. N) {
        SSum[i + 1] = SSum[i] + S[i];
      }
      
      const lim = N * max(SSum[N], 1);
      bool check(long buy) {
        long m = buy;
        foreach (iter; 0 .. lim + 1) {
          const mm = buy + SSum[N] * (m / N) + SSum[cast(int)(m % N)];
          if (mm >= K) {
            return true;
          }
          if (mm == m) {
            return false;
          }
          if (iter == lim) {
            return true;
          }
          m = mm;
        }
        assert(false);
      }
      
      long lo = 0, hi = K;
      for (; lo + 1 < hi; ) {
        const mid = (lo + hi) / 2;
        (check(mid) ? hi : lo) = mid;
      }
      writeln(hi);
    }
  } catch (EOFException e) {
  }
}