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

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int H,W,M; cin >> H >> W >> M;
    vector<string> S(H);
    for(auto &s : S) cin >> s;

    vector<vector<vector<int>>> dist(H,vector<vector<int>>(W,vector<int>(M+1,-1)));
    int sx,sy,gx,gy;
    for(int i=0; i<H; i++) for(int k=0; k<W; k++){
        if(S.at(i).at(k) == 'S') sx = i,sy = k;
        if(S.at(i).at(k) == 'G') gx = i,gy = k;
    }
    queue<tuple<int,int,int>> Q; Q.push({sx,sy,0});
    dist.at(sx).at(sy).at(0) = 0;
    vector<pair<int,int>> dxy = {{-1,0},{0,1},{1,0},{0,-1}};
    while(Q.size()){
        auto [x,y,m] = Q.front(); Q.pop();
        int d = dist.at(x).at(y).at(m);
        if('1' <= S.at(x).at(y) && S.at(x).at(y) <= '9'){
            int v = S.at(x).at(y)-'0';
            if(v != m){
                if(dist.at(x).at(y).at(v) != -1) continue;
                dist.at(x).at(y).at(v) = d,Q.push({x,y,v}); continue;
            }
        }

        for(auto [dx,dy] : dxy){
            int nx = x+dx,ny = y+dy;
            if(nx < 0 || ny < 0 || nx >= H || ny >= W) continue;
            if(S.at(nx).at(ny) == '#') continue;
            if(dist.at(nx).at(ny).at(m) != -1) continue;
            if('a' <= S.at(nx).at(ny) && S.at(nx).at(ny) <= 'i'){
                if(S.at(nx).at(ny)-'a'+1 != m) continue;
            }
            dist.at(nx).at(ny).at(m) = d+1,Q.push({nx,ny,m});
        }
    }
    int answer = 1000000;
    for(auto d : dist.at(gx).at(gy)) if(d != -1) answer = min(answer,d);
    if(answer == 1000000) answer = -1;
    cout << answer << endl;
}