#include <iostream>
#include <algorithm>
#include <utility>
#include <vector>
#include <string>

//#define rep(i, j) for(int i = 0; i < j; ++i)
#define FOR(v, i, j) for(int v = int(i); v < int(j); ++v)
#define MOD 1000000007
//typedef long long ll

using namespace std;
//ios::sync_with_stdio(false);


string want;
int n, x;
int DP[1010][1010][2];

void get_num() {
	int len = want.length();
	FOR(i,0,len) {
		DP[i][0][0] = 0;
		DP[i][0][1] = 0;
	}
	FOR(i,0,len) {
		DP[0][i][0] = 1;
		DP[0][i][1] = 1;
	}
	
	//alg
	FOR(k,1,len+2) {
		FOR(l,k,len+2) {
			FOR(i, 0, 2) {
				if (!i) DP[k][l][0] = DP[k][l-1][0] + DP[k-1][l-1][0];
				else if (want[len-l] == '1') DP[k][l][1] = DP[k][l-1][0] + DP[k-1][l-1][1];
				else DP[k][l][1] = DP[k][l-1][1];
				DP[k][l][i] %= MOD;
			}			
		}
	}
}

char temp[1010];
int main(void){
	cin >> n >> x;
	string want1;
	cin >> want1;
	want = want1;
	int len = want.length();
	bool ok = true;
	FOR(i, 0, len) {
		if (want[i] == '1') {
			ok=false;			
			break;
		}	
	}

		
	//cout << want << endl; //DEBUG
	temp[0] = '0';
	FOR(i, 1, len+1) {
		temp[i] = want[i-1];
	}
	temp[len+1] = 0;
	//cout << string(temp) << endl; //DEBUG
	if (!ok) {
		FOR(i, 0, len) {
			if (temp[len-i] == '1') {
				temp[len-i] = '0';
				break;
			}
			temp[len-i] = '1';
		}
	}
	want = string(temp);
	//cout << want << endl; //DEBUG
	get_num();
	int res1 = DP[x][len+1][1];
	temp[0] = '1';
	if (ok) {
		res1 = 0;
		FOR(i, 0, len+1) {
			if (temp[len-i] == '1') {
				temp[len-i] = '0';
				break;
			}
			temp[len-i] = '1';
		}
	}
	want = string(temp);
	//cout << want << endl; //DEBUG
	get_num();
	int res2 = DP[x][len+1][1];
	
	int res = res2 -res1;
	if (res < 0)
		res += MOD;
	cout << res << endl;
	return 0;
}