#include<bits/stdc++.h>
#define up(a,b,c)for(int a=b;a<=c;++a)
const int N=22e4;
using namespace std;
int n,m,k,f[N],g[N],h[N];
string s;
bool chk(int L)
{
	int cc=0;
	up(i,0,n-1)
	{
		cc+=s[i]=='0';
		if(i>=L-1)g[i-L+1]=cc,cc-=s[i-L+1]=='0';
	}
	fill(f,f+n,m+1);
	copy(g,g+n-L+1,f+L-1);
	up(_,1,k-1)
	{
		int A=m+1,B=m+1;
		up(i,0,n-1)
		{
			h[i]=B;
			if(s[i]=='0')B=min(A,B);
			else B=min(A,B+1);
			A=min(A,f[i]);
		}
		fill(f,f+n,m+1);
		up(i,0,n-L)f[i+L-1]=min(g[i]+h[i],m+1);
	}
	int res=m+1;
	up(i,0,n-1)res=min(res,f[i]);
	return res<=m;
}
int main()
{
	cin>>n>>m>>k>>s;
	int l=0,r=n/k+1;
	while(l+1<r)
	{
		int mid=(l+r)/2;
		if(chk(mid))l=mid;
		else r=mid;
	}
	cout<<(l?l:-1);
	return 0;
}