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

int IleSpotkan(string x)
{
	int ile=0;
	for(int i=0;i<x.size();i++)
	{
		if(x[i]-'0'==2)
		ile++;
		
		if(x[i]-'0'==1)
		ile++;
		
	}
	
	return ile;
}

int IleOminie(string a, int pdp, int kdp, int pdd, int kdd)
{
	int ilep=0;
	for(int i=0;i<pdp;i++){
	if(a[i]-'0'==1)
	ilep++;
	}
	
	for(int i=pdp;i<=kdp;i++){
	if(a[i]-'0'==1||a[i]-'0'==2)
	ilep++;
	}
	
	for(int i=pdd;i<=kdd;i++){
	if(a[i]-'0'==1||a[i]-'0'==2)
	ilep++;
	}
	
	
	for(int i=kdd+1;i<a.size();i++){
	if(a[i]-'0'==1)
	ilep++;
	}
	
	return ilep;
}

int IleRobi(string a, int pdp, int kdp, int pdd, int kdd)
{
	int ilez=0;
	for(int i=0;i<pdp;i++){
	if(a[i]-'0'==3||a[i]-'0'==1)	
	ilez++;	
	}
	for(int i=kdd+1;i<a.size();i++){
	if(a[i]-'0'==3||a[i]-'0'==1)	
	ilez++;	
	}
	
	return ilez;
	
	
}


int main()
{
	std::ios_base::sync_with_stdio(0);

string s;
int n,k,t;
vector <int> vec;
cin>>n>>k>>t>>s; 


if(IleSpotkan(s)<=k)
{
cout<<n;
return 0;
}

int pdp=0;
int kdp=t-1;
int pdd=t;
int kdd=2*t;


while(kdd<=n){
int liczba=IleOminie(s, pdp, kdp, pdd, kdd);

if(liczba>k&&kdp<pdd)
{
	pdd++;
	kdd++;
}
else if(liczba<=k&&kdp+1<pdd)
{
	vec.push_back(IleRobi(s, pdp, kdp, pdd, kdd));
	pdp++;
	kdp++;
}
else if(liczba<=k&&kdp+1==pdd)
{
	vec.push_back(IleRobi(s, pdp, kdp, pdd, kdd));
	pdd++;
	kdd++;
}

}

pdp=0;
kdp=t-1;
pdd=t;
kdd=2*t;
reverse(s.begin(), s.end());

while(kdd<=n){
int liczba=IleOminie(s, pdp, kdp, pdd, kdd);

if(liczba>k&&kdp<pdd)
{
	pdd++;
	kdd++;
}

if(liczba<=k&&kdp+1<pdd)
{
	vec.push_back(IleRobi(s, pdp, kdp, pdd, kdd));
	pdp++;
	kdp++;
}

if(liczba<=k&&kdp+1==pdd)
{
	vec.push_back(IleRobi(s, pdp, kdp, pdd, kdd));
	pdd++;
	kdd++;
}

}



sort(vec.begin(), vec.end(), greater<int>());
if(vec.size()==0)
cout<<"-1";
else
cout<<vec[0];





return 0;	
}