#include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <algorithm>
#include <set>
#include <map>
#include <bitset>
#include <cmath>
#include <functional>
#include <iomanip>
#define vll vector<ll>
#define vvvl vector<vvl>
#define vvl vector<vector<ll>>
#define VV(a, b, c, d) vector<vector<d>>(a, vector<d>(b, c))
#define VVV(a, b, c, d) vector<vvl>(a, vvl(b, vll (c, d)));
#define re(c, b) for(ll c=0;c<b;c++)
#define rep(a,b,c) for(ll a=b;a<c;a++)
#define all(obj) (obj).begin(), (obj).end()
typedef long long int ll;
typedef long double ld;
using namespace std;

void get(vll &a){re(i,a.size()) scanf("%lld",&a[i]);}
void get(vvl &a){re(i,a.size()) re(j,a[0].size()) scanf("%lld",&a[i][j]);}
void print(vll &a){re(i,a.size()) cout<<a[i]<<(i==a.size()-1?"\n":" ");}
void print(vvl &a){re(i,a.size()) re(j,a[0].size())cout<<a[i][j]<<(j==a[0].size()-1?"\n":" ");}

int main() {
  ll n, k;std::cin >> n >> k;
  ll l = 0, r = 10000000000;//box
  string s;std::cin >> s;
  ll S = 0;
  for(auto c:s) S += (c-'0');
  map<ll, ll> mp;
  while(r-l>1){
    ll mid = (l+r)/2;
    ll eat = mid * n, num = mid * S;

    while(num){
      ll pre = num;
      ll x = num/n;
      num %= n;

      if(x){
        num += x*S;
        eat += x*n;
      }else{
        ll idx = 0;
        while(num){
          num--;
          eat++;
          if(s[idx]=='1') num++;
          if(s[idx]=='2') num+=2;
          idx = (idx + 1)%n;
          if(eat>k) break;
        }
        break;
      }
      if(pre>=num) {
        eat = k+1;
        break;
      }
      if(eat>k) break;
    }
    mp[mid] = eat;
    if(eat>k) r = mid;
    else l = mid;
  }

  for(int i=0;i<=n;i++){
    ll eat = mp[l];
    ll num = i;
    ll idx = eat%n;
    while(num){
      num--;
      eat++;
      if(s[idx]=='1') num++;
      if(s[idx]=='2') num+=2;
      idx = (idx+1)%n;
      if(eat>=k) break;
    }
    if(eat>=k){
      std::cout << l*n+i << '\n';
      return 0;
    }
  }
}