#include <algorithm>
#include <iostream>
#include <cstdio>
#include <map>
#include <numeric>
#include <cmath>
#include <set>
#include <sstream>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <complex>
#include <string.h>
#include <unordered_set>
#include <unordered_map>
#include <bitset>
#include <iomanip>
#include <sys/time.h>
#include <random>
using namespace std;

#define endl '\n'
#define ALL(v) (v).begin(), (v).end()
#define RALL(v) (v).rbegin(), (v).rend()
#define UNIQ(v) (v).erase(unique((v).begin(), (v).end()), (v).end())

typedef long long ll;
typedef long double ld;
typedef pair<int, int> P;
typedef complex<double> comp;
typedef vector< vector<ld> > matrix;
struct pairhash {
public:
    template<typename T, typename U>
    size_t operator()(const pair<T, U> &x) const {
	size_t seed = hash<T>()(x.first);
	return hash<U>()(x.second) + 0x9e3779b9 + (seed<<6) + (seed>>2);
    }
};
const int inf = 1e9 + 9;
const ll mod = 1e9 + 7;
const double eps = 1e-8;
const double pi = acos(-1);

int n, k;
string s;

int solve() {
    bool used[n+1];
    int prev[n+1];
    int prev_n[n+1];
    memset(used, false, sizeof(used));
    memset(prev, 0, sizeof(prev));
    memset(prev_n, 0, sizeof(prev_n));
    int res = 0, e = 0, t = 0, f = 0, i = 0;
    bool flag = false;
    while (true) {
        if (e == 0&&!flag) {
            if (t > n) return res;            
            if (used[t]) {
                int d = res - prev[t];
                int di = i - prev_n[t];
                di *= n;
                k -= f;
                res += k / di * d;
                k %= di;
                if (k == 0) return res;
                k += f;
                flag = true;
            } else {
                used[t] = true;
                prev[t] = res;
                prev_n[t] = i;
            }
            i++;
        }
        switch (s[e]) {
        case '0': if (t == 0) {res++;} else {t--;} break;
        case '1': if (t == 0) {res++; t++;} break;
        case '2': if (t== 0) {res++; t+=2;} else {t++;}
        }
        f++;
        e++;
        e%=n;
        if (f == k) return res;
    }
    return -1;
}

void input() {
    cin >> n >> k >> s;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(15);

    input();
    cout << solve() << endl;
}