#include <iostream>
#include <vector>
#include <string>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <algorithm>	// require sort next_permutation count __gcd reverse etc.
#include <cstdlib>	// require abs exit atof atoi 
#include <cstdio>		// require scanf printf
#include <functional>
#include <numeric>	// require accumulate
#include <cmath>		// require fabs
#include <climits>
#include <limits>
#include <cfloat>
#include <iomanip>	// require setw
#include <sstream>	// require stringstream 
#include <cstring>	// require memset
#include <cctype>		// require tolower, toupper
#include <fstream>	// require freopen
#include <ctime>		// require srand
#define rep(i,n) for(int i=0;i<(n);i++)
#define ALL(A) A.begin(), A.end()

using namespace std;

typedef long long ll;
typedef pair<int, int> P;

// シミュレーションで求める
string smulation (int & lucky, int & eaten, int & buy, string S, int N, int K ){
	string res = "";
	for (int i = 0; i < N;  i++ ){
		int curr = (S[i] - '0' );	// 現在のアイスバーの判定
		if (lucky > 0 ){
			res += 'x';//cerr << 'x'; アイスバーを買わなくて良い
			lucky--;
		}else{
			res += 'o';//cerr << 'o'; アイスバーを買う必要がある
			buy++;	
		} // end if
		eaten++;
		if (eaten == K ){
			return res;
		} // end if
		lucky += curr;
	} // end for

	return res;
}

int solve (int N, int K, string S ){
	int lucky = 0, eaten = 0, buy = 0;
	int res = 0;
	string t = smulation (lucky, eaten, buy, S, N, K );
	res += buy;
//	cerr << t << " buy: " << buy << " lucky: " << lucky << endl;
	if (N < K ){
		rep (i, N )
			if (t[i] == 'o' && lucky ) t[i] = 'x', lucky--;
//		cerr << t << endl;
		res += (int)count (ALL (t ), 'o' )*(K/N-1);
		if(K % N != 0 ){
			res += (int)count (t.begin(), t.begin()+(K%N), 'o' );
		} // end if
	} // end if

	return res;
}

int main()
{
	ios_base::sync_with_stdio(0);
	int N, K; cin >> N >> K;
	string S; cin >> S;

	int res = solve (N, K, S );
	cout << res << endl;

	return 0;
}