#include <bits/stdc++.h>
//#include <math.h>
using namespace std;

#define INF 1.1e9
#define LINF 1.1e18
#define FOR(i,a,b) for (int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
#define pb push_back
#define pf push_front
#define fi first
#define se second
#define BIT(x,n) bitset<n>(x)
#define PI 3.14159265358979323846

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

//-----------------------------------------------------------------------------

int n,k;
string s;
int sum[2][55];

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	cin>>n>>k>>s;
	int cnt=0,tmp=0;
	REP(i,n) {
		if(tmp) tmp--;
		else cnt++;
		tmp+=s[i]-'0';
		sum[0][i]=cnt;
	}
	if(k<=n) {
		cout<<sum[0][k-1]<<endl;
		return 0;
	}
	cnt=0;
	REP(i,n) {
		if(tmp) tmp--;
		else cnt++;
		tmp+=s[i]-'0';
		sum[1][i]=cnt;
	}
	ll ans=0;
	ans+=sum[0][n-1];
	ans+=(k/n-1)*sum[1][n-1];
	if(k%n) ans+=sum[1][(k-1)%n];
	cout<<ans<<endl;


	return 0;
}