#include<bits/stdc++.h>
using namespace std;
#define int long long
#define pb push_back
#define MEM(a,x) memset(a,x,sizeof(a));
#define all(x) x.begin(),x.end()
#define rep(i,a,b) for(int i=a;i<(b);i++)
#define Rep(i,a,b) for(int i=a;i>=(b);i--)
typedef vector<int> vi;
const int N=2e5+5,inf=1e9;
int n,m,k;
string s;
int dp[6][N];
bool check(int x){
	MEM(dp,0x3f);
	dp[0][0]=0;
	int p=0,cnt=0;
	vi mn(6,inf);mn[0]=0;
	rep(i,1,x+1)cnt+=s[i]=='0';
	rep(i,x+1,n+2){
		rep(j,1,k+1)dp[j][i]=min(dp[j][i],mn[j-1]+cnt+(s[i]=='1'));
		cnt-=(s[p++]=='0'),cnt+=(s[i]=='0');
		rep(j,0,k+1)mn[j]=min(dp[j][p],mn[j]);
	}
	return *min_element(dp[k]+1,dp[k]+n+2)<=m;
}
signed main(){
	ios::sync_with_stdio(0);
	cin.tie(0),cout.tie(0);
	cin>>n>>m>>k>>s;
	s='0'+s+'0';
	int l=0,r=n;
	while(l<r){
		int md=(l+r+1)/2;
		if(check(md))l=md;
		else r=md-1;
	}
	cout<<(!l?-1:l)<<endl;
	return 0;
}