#include <iostream>
#include <bits/stdc++.h>
#define ll long long
using namespace std;
int n,k;
const int MOD = 1000000007;
ll binom[2222][2222];
char S[2222];
ll dp[1222][1222][2];
ll pow2m[1222];
ll smaller(int pos, int has, int isok) {
	if(pos == n) {
		return has == k && isok;
	}
	if(dp[pos][has][isok] == -1) {
		ll& ans = dp[pos][has][isok];
		ans = 0;
		if(S[pos] == '0') {
			if(isok)
				ans = smaller(pos+1, has+1, isok);
			ans += smaller(pos+1, has, isok);
		} else {
			ans = smaller(pos+1, has, 1);
			ans += smaller(pos+1, has+1, isok);

		}
		ans %= MOD;
	}
	return dp[pos][has][isok];
}
string S2() {
	string res;
	int carry = 1;
	for(int i = n-1; i >= 0; i--) {
		int x = carry+(S[i]-'0')+1;
		carry = x/2;
		res.push_back((x%2)+'0');
	}
	if(carry) res.push_back('1');
	reverse(res.begin(), res.end());
	return res;
}
int main() {
	memset(dp, -1, sizeof(dp));
	scanf("%d%d", &n, &k);
	scanf("%s", S);
	pow2m[0] = 1;
	for(int i = 1; i < 1222; i++)
		pow2m[i] = (pow2m[i-1]*2)%MOD;
	binom[1][0] = 1;
	binom[1][1] = 1;
	for(int i = 2; i <= 1200; i++) {
		binom[i][0] = binom[i][i] = 1;
		for(int j = 1; j < i; j++)
			binom[i][j] = (binom[i-1][j-1]+binom[i-1][j])%MOD;
	}
	ll t1 = smaller(0, 0, 0);
	memset(dp, -1, sizeof(dp));
	string Sx = S2();
	for(int i = 0; i < Sx.size(); i++) S[i] = Sx[i];
	if(n != Sx.size()) n++;
	ll t2 = smaller(0, 0, 0);
//	printf("%s\n", S2().c_str());	
//	printf("%lld %lld\n", t1, t2);
	ll ans = ((t2-t1)%MOD+MOD)%MOD;
	printf("%lld\n", ans);

//	ll res = 
	
	
	/*binom[n][k];
	if(S[0] == '1') {
		res = (binom[n][k]+binom[n][k-1])%MOD;
	}
	scanf("%s", S);
	printf("%lld\n", res);
	printf("%lld\n", smaller(0, 0, 0));
	res = (res-smaller(0, 0, 0)+MOD)%MOD;
	printf("%lld\n", res);
*/
	
	return 0;

}