#include <bits/stdc++.h>
using namespace std;
#define int long long   // <-----!!!!!!!!!!!!!!!!!!!

#define rep(i,n) for (int i=0;i<(n);i++)
#define rep2(i,a,b) for (int i=(a);i<(b);i++)
#define rrep(i,n) for (int i=(n)-1;i>=0;i--)
#define rrep2(i,a,b) for (int i=(a)-1;i>=b;i--)
#define chmin(a,b) (a)=min((a),(b));
#define chmax(a,b) (a)=max((a),(b));
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define printV(v) cerr<<(#v)<<":";for(auto(x):(v)){cerr<<" "<<(x);}cerr<<endl;
#define printVS(vs) cerr<<(#vs)<<":"<<endl;for(auto(s):(vs)){cerr<<(s)<< endl;}
#define printVV(vv) cerr<<(#vv)<<":"<<endl;for(auto(v):(vv)){for(auto(x):(v)){cerr<<" "<<(x);}cerr<<endl;}
#define printP(p) cerr<<(#p)<<(p).first<<" "<<(p).second<<endl;
#define printVP(vp) cerr<<(#vp)<<":"<<endl;for(auto(p):(vp)){cerr<<(p).first<<" "<<(p).second<<endl;}

inline void output(){ cerr << endl; }
template<typename First, typename... Rest>
inline void output(const First& first, const Rest&... rest) {
    cerr << first << " "; output(rest...);
}

using ll = long long;
using Pii = pair<int, int>;
using TUPLE = tuple<int, int, int>;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
const int inf = 1ll << 60;
const int mod = 1e9 + 7;
using Graph = vector<vector<int>>;

int H, W, A;
vector<string> s(H);
int sx, sy, gx, gy;
const int MAX_V = 4*11*11*100*100;
int d[MAX_V];

const int dx[4] = { 1, 0, -1,  0};
const int dy[4] = { 0, 1,  0, -1};

bool inside(int x, int y) {
    return 0 <= x && x < H && 0 <= y && y < W;
}

struct Node {
    int x, y, p, q, k, id;
    Node(){}
    Node(int _x, int _y, int _p, int _q, int _k) : x(_x), y(_y), p(_p), q(_q), k(_k), id(-1) {
        if (!inside(x, y)) return;
        if (p < 0 || q < 0) return;
        if (s[x][y] == '#') return;
        if (s[x][y] == 'S' && k == 2) return;
        id = 4*11*11*100*x + 4*11*11*y + 4*11*p + 4*q + k;
    }
    Node(int _id) : id(_id) {
        k = _id % 4; _id /= 4;
        q = _id % 11; _id /= 11;
        p = _id % 11; _id /= 11;
        y = _id % 100; _id /= 100;
        x = _id;
    }
    void print() {
        output(x, y, p, q, k, id);
    }
};

int dijkstra() {
    using State = pair<int, int>;
    priority_queue<State, vector<State>, greater<State>> pq;   // cost, vertex
    fill(d, d + MAX_V, inf);

    Node ns(sx, sy, A, A, 0);
    d[ns.id] = 0;
    pq.push(State(0, ns.id));

    while (!pq.empty()) {
        int cost, id;
        tie(cost, id) = pq.top(); pq.pop();
        if (d[id] < cost) continue;
        Node u(id);

        int x = u.x;
        int y = u.y;
        int p = u.p;
        int q = u.q;
        int k = u.k;

        if (x == gx && y == gy) {
            return cost;
        }

        vector<pair<Node, int>> cands; // v, cost(u->v)

        if (s[x][y] == 'S') {
            cands.emplace_back(Node(x + dx[k], y + dy[k], p, q, k), 0);
        }
        else if (k == 0) {
            cands.emplace_back(Node(x, y - 1, p, q - 1, 3), 1);
            cands.emplace_back(Node(x, y + 1, p - 1, q, 1), 1);
            cands.emplace_back(Node(x + 1, y, p, q, 0), 0);
        }
        else if (k == 1) {
            cands.emplace_back(Node(x - 1, y, p, q - 1, 2), 1);
            cands.emplace_back(Node(x + 1, y, p - 1, q, 0), 1);
            cands.emplace_back(Node(x, y + 1, p, q, 1), 0);
        }
        else if (k == 2) {
            cands.emplace_back(Node(x, y - 1, p - 1, q, 3), 1);
            cands.emplace_back(Node(x, y + 1, p, q - 1, 1), 1);
            cands.emplace_back(Node(x - 1, y, p, q, 2), 0);
        }
        else if (k == 3) {
            cands.emplace_back(Node(x - 1, y, p - 1, q, 2), 1);
            cands.emplace_back(Node(x + 1, y, p, q - 1, 0), 1);
            cands.emplace_back(Node(x, y - 1, p, q, 3), 0);
        }

        for (const auto& p : cands) {
            Node v;
            int c;
            tie(v, c) = p;
            if (v.id == -1) continue;
            if (d[v.id] > d[u.id] + c) {
                d[v.id] = d[u.id] + c;
                pq.push(State(d[v.id], v.id));
            }
        }
    }

    return -1;
}

signed main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);

    cin >> H >> W >> A;
    s.resize(H);
    rep(i, H) {
        cin >> s[i];
        rep(j, W) {
            if (s[i][j] == 'S') {
                sx = i; sy = j;
            }
            if (s[i][j] == 'G') {
                gx = i; gy = j;
            }
        }
    }

    cout << dijkstra() << endl;
}