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#include<bits/stdc++.h>
bool Mbg;
using namespace std;
#define vec vector
#define pb push_back
#define eb emplace_back
#define siz(vec) (int)((vec).size())
#define all(vec) (vec).begin(),(vec).end()
template<class T>
void operator +=(vec<T> &a,T b){a.push_back(b);}
#define pii pair<int,int>
#define x first
#define y second
#define mp make_pair
#define exc(expr) if(expr)continue;
#define stop(expr) if(expr)break;
#define ret(expr) if(expr)return;
#define deb(var) cerr<<#var<<'='<<(var)<<"; "
#define debl(var) cerr<<#var<<'='<<(var)<<";\n"
#define ins insert
#define era erase
#define lb lower_bound
#define ub upper_bound
#define int long long
#define inf (long long)(1e18)
template<class T>
bool Min(T &x,T y){return x>y?x=y,1:0;}
template<class T>
bool Max(T &x,T y){return x<y?x=y,1:0;}
const int mod=998244353;
void Add(int &x,int y){x=x+y<mod?x+y:x+y-mod;}
void Dec(int &x,int y){x=x>=y?x-y:x-y+mod;}
int fpm(int x,int y){
    int ans=1;for(;y;y>>=1,x=1ll*x*x%mod)if(y&1)ans=1ll*x*ans%mod;return ans;
}

int n,k,t,c0[8010],c1[8010];
char s[8010];
void work(){
    cin>>n>>k>>t>>s;
    for(int i=1;i<=n;i++){
        c0[i]=c0[i-1]+(s[i-1]=='1');
        c1[i]=c1[i-1]+(s[i-1]=='2');
    }

    k=max(0ll,c0[n]+c1[n]-k);

    int ans=-inf;
    for(int i=1;i<=n-t+1;i++){
        for(int j=i+t;j<=n-t+1;j++){
            // [i,i+t-1]
            // [j,j+t-1]

            int c=c0[j-1]-c0[i+t-1]+c1[j-1]-c1[i+t-1];
            
            if(c+c1[i-1]+c1[n]-c1[j+t-1]>=k){
                Max(ans,i-1+n-(j+t-1)-max(k-c,0ll));
            }
        }
    }

    if(c1[n]>=k){
        Max(ans,n-k);
    }

    if(ans<0){
        cout<<"-1\n";
    }else{
        cout<<ans<<'\n';
    }
}
bool Med;
signed main(){
    ios::sync_with_stdio(0),
    cin.tie(0),cout.tie(0);
    int T=1;while(T--)work();
    // cerr<<"Time: "<<clock()<<" ms;\n";
    // cerr<<"Memory: "<<abs(&Med-&Mbg)/1024.0/1024.0<<" MiB.\n";
}
/*
- CONTINUE, NON-STOPPING, FOR THE FAITH
- START TYPING IF YOU DON'T KNOW WHAT TO DO
- STOP TYPING IF YOU DON'T KNOW WHAT YOU'RE DOING
*/