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

using ll=long long;
//#define int ll

#define rng(i,a,b) for(int i=int(a);i<int(b);i++)
#define rep(i,b) rng(i,0,b)
#define gnr(i,a,b) for(int i=int(b)-1;i>=int(a);i--)
#define per(i,b) gnr(i,0,b)
#define pb push_back
#define eb emplace_back
#define a first
#define b second
#define bg begin()
#define ed end()
#define all(x) x.bg,x.ed
#ifdef LOCAL
#define dmp(x) cerr<<__LINE__<<" "<<#x<<" "<<x<<endl
#else
#define dmp(x) void(0)
#endif

template<class t,class u> void chmax(t&a,u b){if(a<b)a=b;}
template<class t,class u> void chmin(t&a,u b){if(b<a)a=b;}

template<class t> using vc=vector<t>;
template<class t> using vvc=vc<vc<t>>;

using pi=pair<int,int>;
using vi=vc<int>;

template<class t,class u>
ostream& operator<<(ostream& os,const pair<t,u>& p){
	return os<<"{"<<p.a<<","<<p.b<<"}";
}

template<class t> ostream& operator<<(ostream& os,const vc<t>& v){
	os<<"{";
	for(auto e:v)os<<e<<",";
	return os<<"}";
}

#define mp make_pair
#define mt make_tuple
#define one(x) memset(x,-1,sizeof(x))
#define zero(x) memset(x,0,sizeof(x))
#ifdef LOCAL
void dmpr(ostream&os){os<<endl;}
template<class T,class... Args>
void dmpr(ostream&os,const T&t,const Args&... args){
	os<<t<<" ";
	dmpr(os,args...);
}
#define dmp2(...) dmpr(cerr,"Line:",__LINE__,##__VA_ARGS__)
#else
#define dmp2(...) void(0)
#endif

using uint=unsigned;
using ull=unsigned long long;

template<class t,size_t n>
ostream& operator<<(ostream&os,const array<t,n>&a){
	return os<<vc<t>(all(a));
}

template<int i,class T>
void print_tuple(ostream&,const T&){
}

template<int i,class T,class H,class ...Args>
void print_tuple(ostream&os,const T&t){
	if(i)os<<",";
	os<<get<i>(t);
	print_tuple<i+1,T,Args...>(os,t);
}

template<class ...Args>
ostream& operator<<(ostream&os,const tuple<Args...>&t){
	os<<"{";
	print_tuple<0,tuple<Args...>,Args...>(os,t);
	return os<<"}";
}

void print(ll x,int suc=1){
	cout<<x;
	if(suc==1)
		cout<<"\n";
	if(suc==2)
		cout<<" ";
}

ll read(){
	ll i;
	cin>>i;
	return i;
}

vi readvi(int n,int off=0){
	vi v(n);
	rep(i,n)v[i]=read()+off;
	return v;
}

template<class T>
void print(const vector<T>&v,int suc=1){
	rep(i,v.size())
		print(v[i],i==int(v.size())-1?suc:2);
}

string readString(){
	string s;
	cin>>s;
	return s;
}

template<class T>
T sq(const T& t){
	return t*t;
}

//#define CAPITAL
void yes(bool ex=true){
	#ifdef CAPITAL
	cout<<"YES"<<endl;
	#else
	cout<<"Yes"<<endl;
	#endif
	if(ex)exit(0);
}
void no(bool ex=true){
	#ifdef CAPITAL
	cout<<"NO"<<endl;
	#else
	cout<<"No"<<endl;
	#endif
	if(ex)exit(0);
}
void possible(bool ex=true){
	#ifdef CAPITAL
	cout<<"POSSIBLE"<<endl;
	#else
	cout<<"Possible"<<endl;
	#endif
	if(ex)exit(0);
}
void impossible(bool ex=true){
	#ifdef CAPITAL
	cout<<"IMPOSSIBLE"<<endl;
	#else
	cout<<"Impossible"<<endl;
	#endif
	if(ex)exit(0);
}

constexpr ll ten(int n){
	return n==0?1:ten(n-1)*10;
}

const ll infLL=LLONG_MAX/3;

#ifdef int
const int inf=infLL;
#else
const int inf=INT_MAX/2-100;
#endif

int topbit(signed t){
	return t==0?-1:31-__builtin_clz(t);
}
int topbit(ll t){
	return t==0?-1:63-__builtin_clzll(t);
}
int botbit(signed a){
	return a==0?32:__builtin_ctz(a);
}
int botbit(ll a){
	return a==0?64:__builtin_ctzll(a);
}
int popcount(signed t){
	return __builtin_popcount(t);
}
int popcount(ll t){
	return __builtin_popcountll(t);
}
bool ispow2(int i){
	return i&&(i&-i)==i;
}
int mask(int i){
	return (int(1)<<i)-1;
}

bool inc(int a,int b,int c){
	return a<=b&&b<=c;
}

template<class t> void mkuni(vc<t>&v){
	sort(all(v));
	v.erase(unique(all(v)),v.ed);
}

ll rand_int(ll l, ll r) { //[l, r]
	#ifdef LOCAL
	static mt19937_64 gen;
	#else
    static random_device rd;
    static mt19937_64 gen(rd());
    #endif
    return uniform_int_distribution<ll>(l, r)(gen);
}

template<class t>
int lwb(const vc<t>&v,const t&a){
	return lower_bound(all(v),a)-v.bg;
}

const int smax=20;
int dp[1<<smax][smax];

signed main(){
	cin.tie(0);
	ios::sync_with_stdio(0);
	cout<<fixed<<setprecision(20);
	
	int h,w,tar;cin>>h>>w>>tar;
	vc<string> z(h);
	rep(i,h)cin>>z[i];
	auto getdist=[&](int ry,int rx){
		vvc<int> dist(h,vi(w,inf));
		const int dyx[]{-1,0,1,0,-1};
		queue<pi> pos;
		auto reach=[&](int y,int x,int d){
			if(y<0||y>=h||x<0||x>=w)return;
			if(z[y][x]=='#')return;
			if(dist[y][x]!=inf)return;
			dist[y][x]=d;
			pos.emplace(y,x);
		};
		reach(ry,rx,0);
		while(pos.size()){
			int y,x;tie(y,x)=pos.front();pos.pop();
			rep(k,4)
				reach(y+dyx[k],x+dyx[k+1],dist[y][x]+1);
		}
		return dist;
	};
	vc<pi> aps;
	rep(i,h)rep(j,w)if(z[i][j]=='a'){
		aps.eb(i,j);
	}
	int s=aps.size();
	rep(bit,1<<s)rep(i,s)dp[bit][i]=inf;
	{
		vvc<int> dist;
		rep(i,h)rep(j,w)if(z[i][j]=='s')
			dist=getdist(i,j);
		rep(i,s)
			dp[1<<i][i]=dist[aps[i].a][aps[i].b];
	}
	vvc<int> ds(s,vi(s));
	rep(i,s){
		auto dist=getdist(aps[i].a,aps[i].b);
		rep(j,s)
			ds[i][j]=dist[aps[j].a][aps[j].b];
	}
	rng(bit,1,1<<s)rep(i,s)if(dp[bit][i]<inf){
		rep(j,s)if((bit&1<<j)==0)
			chmin(dp[bit|1<<j][j],dp[bit][i]+ds[i][j]);
	}
	int ans=inf;
	{
		vvc<int> dist;
		rep(i,h)rep(j,w)if(z[i][j]=='e')
			dist=getdist(i,j);
		rep(bit,1<<s)if(popcount(bit)>=tar)rep(i,s)
			chmin(ans,dp[bit][i]+dist[aps[i].a][aps[i].b]);
	}
	if(ans>=inf)ans=-1;
	print(ans);
}



Measured memory_bytes: 89736