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

template<class T>
bool chmax(T& a, const T& b) {
    if (a < b) { a = b; return true; }
    return false;
}
template<class T>
bool chmin(T& a, const T& b) {
    if (b < a) { a = b; return true; }
    return false;
}

// std::vector Declaration
template<typename T>
vector<T> make_v(size_t a) { return vector<T>(a); }
template<typename T, typename... Ts>
auto make_v(size_t a, Ts... ts) {
    return vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}

// std::vector Declaration and Initialization
template<typename T>
vector<T> make_vector(size_t a, T x) { return vector<T>(a, x); }
template<typename T, typename U, typename... Ts>
auto make_vector(size_t a, U b, Ts... ts) {
    return vector<decltype(make_vector<T>(b,ts...))>(a, make_vector<T>(b, ts...));
}

// std::vector Input
template<typename T>
istream& operator>>(istream& is, vector<T>& v) {
    for (auto &e : v) is >> e;
    return is;
}

// std::vector Debug
template<typename T>
ostream& operator<<(ostream& os, const vector<T>& v) {
    os << "[";
    bool a = 1;
    for (auto e : v) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "]";
    return os;
}

// std::array Debug
template<typename T, size_t n>
ostream& operator<<(ostream& os, const array<T, n>& v) {
    os << "[";
    bool a = 1;
    for (auto e : v) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "]";
    return os;
}

// std::deque Debug
template<typename T>
ostream& operator<<(ostream& os, const deque<T>& d) {
    os << "[";
    bool a = 1;
    for (auto e : d) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "]";
    return os;
}

// std::pair Debug
template<typename T, typename U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
    os << "(" << p.first << " " << p.second << ")";
    return os;
}

// std::set Debug
template<typename T>
ostream& operator<<(ostream& os, const set<T>& st) {
    os << "{";
    bool a = 1;
    for (auto e : st) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "}";
    return os;
}

// std::multiset Debug
template<typename T>
ostream& operator<<(ostream& os, const multiset<T>& st) {
    os << "{";
    bool a = 1;
    for (auto e : st) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "}";
    return os;
}

// std::map Debug
template<typename T, typename U>
ostream& operator<<(ostream& os, const map<T, U>& mp) {
    os << "{";
    bool a = 1;
    for (auto e : mp) {
        os << (a ? "" : " ");
        os << e.first << ":" << e.second;
        a = 0;
    }
    os << "}";
    return os;
}

// std::tuple Debug
template<int N, class Tuple>
void out(ostream& os, const Tuple& t){}
template<int N, class Tuple, class H, class ...Ts>
void out(ostream& os, const Tuple& t) {
    if (N) os << " ";
    os << get<N>(t);
    out<N+1,Tuple,Ts...>(os, t);
}
template<class ...Ts>
ostream& operator<<(ostream& os, const tuple<Ts...>& t) {
    os << "(";
    out<0,tuple<Ts...>,Ts...>(os, t);
    os << ")";
    return os;
}

// Debug
#define DUMP(x) cerr<<#x<<" = "<<(x)<<endl

// Weighted edge
template<typename T>
struct edge {
    int src, to;
    T cost;

    edge() {}
    edge(int to, T cost) : src(-1), to(to), cost(cost) {}
    edge(int src, int to, T cost) : src(src), to(to), cost(cost) {}

    friend ostream& operator<<(ostream& os, const edge& e) {
        return os << "(" << e.src << "->" << e.to << ":" << e.cost << ")";
    }
};

using LL = int64_t;

#define fs first
#define sc second

const int64_t MOD = 1e9+7;


int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);

    int n, m, a; cin >> n >> m >> a;
    vector<string> s(n);
    int si, sj, gi, gj;
    for (int i = 0; i < n; ++i) {
        cin >> s[i];
        for (int j = 0; j < m; ++j) {
            if (s[i][j] == 'S') si = i, sj = j;
            if (s[i][j] == 'G') gi = i, gj = j;
        }
    }

    if (n <= si+1 or s[si+1][sj] == '#') {
        cout << -1 << endl;
        return 0;
    }

    using data = tuple<int,int,int,int,int>;

    deque<data> deq;
    deq.push_front(make_tuple(si+1,sj,0,a,a));

    map<data,bool> used;

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

    while (!deq.empty()) {
        int i, j, d, p, q;
        tie(i,j,d,p,q) = deq.front();
        deq.pop_front();

        if (i == gi and j == gj) {
            cout << 2*a - (p+q) << endl;
            return 0;
        }

        for (int k = 0; k < 4; ++k) {
            int y = i + dy[k], x = j + dx[k];
            if (y < 0 or n <= y or x < 0 or m <= x
                    or s[y][x] == '#') continue;
            if (s[y][x] == 'S' and k == 2) continue;
            if (d == k) {
                auto tp = make_tuple(y,x,d,p,q);
                if (!used[tp]) {
                    deq.push_front(tp);
                    used[tp] = true;
                }
            } else if ((d+1)%4 == k) {
                if (s[i][j] == 'S') continue;
                if (d & 1) {
                    if (q == 0) continue;
                    auto tp = make_tuple(y,x,k,p,q-1);
                    if (!used[tp]) {
                        deq.push_back(tp);
                        used[tp] = true;
                    }
                } else {
                    if (p == 0) continue;
                    auto tp = make_tuple(y,x,k,p-1,q);
                    if (!used[tp]) {
                        deq.push_back(tp);
                        used[tp] = true;
                    }
                }
            } else if ((d+3)%4 == k) {
                if (s[i][j] == 'S') continue;
                if (d & 1) {
                    if (p == 0) continue;
                    auto tp = make_tuple(y,x,k,p-1,q);
                    if (!used[tp]) {
                        deq.push_back(tp);
                        used[tp] = true;
                    }
                } else {
                    if (q == 0) continue;
                    auto tp = make_tuple(y,x,k,p,q-1);
                    if (!used[tp]) {
                        deq.push_back(tp);
                        used[tp] = true;
                    }
                }
            }
        }
    }

    cout << -1 << endl;

    return 0;
}



Measured memory_bytes: 8268