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

int main(){
  int inf=2e9;
  vector<int> dy={1,0,-1,0},dx={0,1,0,-1};
  int h,w,m;
  cin>>h>>w>>m;
  vector<string> s(h);
  int sx,sy,gx,gy;
  for (int i=0;i<h;i++){
    cin>>s[i];
    for (int j=0;j<w;j++){
      char c=s[i][j];
      if (c=='S') sy=i,sx=j;
      if (c=='G') gy=i,gx=j;
    }
  }
  vector dist(h,vector(w,vector<int>(m+1,inf)));
  dist[sy][sx][0]=0;
  queue<tuple<int,int,int>> q;
  q.push({sy,sx,0});
  while (!q.empty()){
    auto [i,j,k]=q.front();
    q.pop();
    for (int d=0;d<4;d++){
      int ny=i+dy[d],nx=j+dx[d];
      int nk=k;
      if (!(0<=ny&&ny<h&&0<=nx&&nx<w)) continue;
      char c=s[ny][nx];
      if (c=='#') continue;
      if ('1'<=c&&c<='9') nk=c-'0';
      if ('a'<=c&&c<='i'){
        int k2=c-'a'+1;
        if (k!=k2) continue;
      }
      if (dist[ny][nx][nk]!=inf) continue;
      dist[ny][nx][nk]=dist[i][j][k]+1;
      q.push({ny,nx,nk});
    }
  }
  int ans=inf;
  for (int i=0;i<=m;i++) ans=min(ans,dist[gy][gx][i]);
  if (ans==inf) cout<<-1<<endl;
  else cout<<ans<<endl;
}