#include <bits/stdc++.h>
using namespace std;
using lint = long long;
const lint mod = 998244353;
#define all(x) (x).begin(), (x).end()
#define bitcount(n) __builtin_popcountl((lint)(n))
#define fcout cout << fixed << setprecision(15)
#define highest(x) (63 - __builtin_clzl(x))
template<class T> inline void YES(T condition){ if(condition) cout << "YES" << endl; else cout << "NO" << endl; }
template<class T> inline void Yes(T condition){ if(condition) cout << "Yes" << endl; else cout << "No" << endl; }
template<class T = string, class U = char>int character_count(T text, U character){ int ans = 0; for(U i: text){ ans += (i == character); } return ans; }
lint power(lint base, lint exponent, lint module){ if(exponent % 2){ return power(base, exponent - 1, module) * base % module; }else if(exponent){ lint root_ans = power(base, exponent / 2, module); return root_ans * root_ans % module; }else{ return 1; }}
struct position{ int y, x; }; position mv[4] = {{0, -1}, {1, 0}, {0, 1}, {-1, 0}}; // double euclidean(position first, position second){ return sqrt((second.x - first.x) * (second.x - first.x) + (second.y - first.y) * (second.y - first.y)); }
template<class T, class U> string to_string(pair<T, U> x){ return to_string(x.first) + "," + to_string(x.second); } string to_string(string x){ return x; }
template<class itr> void array_output(itr start, itr goal){ string ans; for(auto i = start; i != goal; i++) ans += to_string(*i) + " "; if(!ans.empty()) ans.pop_back(); cout << ans << endl; }
template<class itr> void cins(itr first, itr last){ for(auto i = first; i != last; i++){ cin >> (*i); } }
template<class T> T gcd(T a, T b){ if(a && b){ return gcd(min(a, b), max(a, b) % min(a, b)); }else{ return a; }} template<class T> T lcm(T a, T b){ return a / gcd(a, b) * b; }
struct combination{ vector<lint> fact, inv; combination(int sz) : fact(sz + 1), inv(sz + 1){ fact[0] = 1; for(int i = 1; i <= sz; i++){ fact[i] = fact[i - 1] * i % mod; } inv[sz] = power(fact[sz], mod - 2, mod); for(int i = sz - 1; i >= 0; i--){ inv[i] = inv[i + 1] * (i + 1) % mod; } } lint C(int p, int q) const{ if(q < 0 || p < q) return 0; return (fact[p] * inv[q] % mod * inv[p - q] % mod); } };
template<class itr> bool next_sequence(itr first, itr last, int max_bound){ itr now = last; while(now != first){ now--; (*now)++; if((*now) == max_bound){ (*now) = 0; }else{ return true; } } return false; }
template<class itr, class itr2> bool next_sequence2(itr first, itr last, itr2 first2, itr2 last2){ itr now = last; itr2 now2 = last2; while(now != first){ now--, now2--; (*now)++; if((*now) == (*now2)){ (*now) = 0; }else{ return true; } } return false; }

string grid[1003];
int dist[1003][1003];

int H, W, K;

int apple_size;
vector<vector<int>> apple;

int dp[21][1 << 21];

int move(int now, int where){
    if(dp[now][where] != -1){
        return dp[now][where];
    }
    if(bitcount(where) == K){
        if(apple[now][apple_size + 1] != -1){
            return dp[now][where] = apple[now][apple_size + 1];
        }else{
            return dp[now][where] = 1e9;
        }
    }
    int ans = 1e9;
    for(int i = 0; i < apple_size; i++){
        if(apple[now][i] == -1){
            continue;
        }
        if((where >> i) & 1){
            continue;
        }
        ans = min(ans, move(i, where | (1 << i)) + apple[now][i]);
    }
    return dp[now][where] = ans;
}

int main(){
    scanf("%d %d %d\n", &H, &W, &K);
    for(int i = 0; i < H; i++){
        grid[i].resize(W);
        for(int j = 0; j < W; j++){
            scanf("%c", &grid[i][j]);
        }
        cin.ignore();
    }
    vector<position> pos;
    position start, goal;
    for(int i = 0; i < H; i++){
        for(int j = 0; j < W; j++){
            if(grid[i][j] == 'a'){
                pos.push_back({i, j});
            }else if(grid[i][j] == 's'){
                start = {i, j};
            }else if(grid[i][j] == 'e'){
                goal = {i, j};
            }
        }
    }
    apple_size = int(pos.size());
    pos.push_back(start);
    pos.push_back(goal);
    apple.resize(pos.size(), vector<int>(pos.size()));
    int i_cnt = 0;
    for(position i: pos){
        for(int i = 0; i < 1003; i++){
            for(int j = 0; j < 1003; j++){
                dist[i][j] = -1;
            }
        }
        queue<position> pathes;
        pathes.push(i);
        dist[i.y][i.x] = 0;
        while(!pathes.empty()){
            auto top = pathes.front();
            pathes.pop();
            for(position j: mv){
                int next_y = top.y + j.y;
                int next_x = top.x + j.x;
                if(0 <= next_y && next_y < H && 0 <= next_x && next_x < W){
                    if(dist[next_y][next_x] == -1 && grid[next_y][next_x] != '#'){
                        dist[next_y][next_x] = dist[top.y][top.x] + 1;
                        pathes.push({next_y, next_x});
                    }
                }
            }
        }
        int j_cnt = 0;
        for(position j: pos){
            apple[i_cnt][j_cnt] = dist[j.y][j.x];
            j_cnt++;
        }
        i_cnt++;
    }
    /*for(auto i: apple){
        array_output(all(i));
    }*/
    memset(dp, -1, sizeof(dp));
    int ans = move(apple_size, 0);
    if(ans > 1e9 - 100){
        printf("%d\n", -1);
    }else{
        printf("%d\n", ans);
    }
    /*cout << ans << endl;
    cout << apple_size << " " << apple.size() << endl;*/
}



Measured memory_bytes: 180120