#include<bits/stdc++.h>
using namespace std;
int main(){
  int h,w,m;
  cin>>h>>w>>m;
  string s[h];
  for(int i=0;i<h;i++) cin>>s[i];
  vector<vector<vector<int>>> d(h,vector<vector<int>>(w,vector<int>(m+1,-1)));
  int si,sj,gi,gj;
  for(int i=0;i<h;i++) for(int j=0;j<w;j++){
    if(s[i][j]=='S'){
      si=i;
      sj=j;
    }
    if(s[i][j]=='G'){
      gi=i;
      gj=j;
    }
  }
  d[si][sj][0]=0;
  queue<tuple<int,int,int>> Q;
  Q.push({si,sj,0});
  int dx[]{1,0,-1,0},dy[]{0,1,0,-1};
  while(!Q.empty()){
    auto [i,j,k]=Q.front();
    Q.pop();
    for(int l=0;l<4;l++){
      int ni=i+dx[l],nj=j+dy[l];
      if(ni<0||ni>=h||nj<0||nj>=w) continue;
      if(s[ni][nj]=='#') continue;
      int nk=k;
      if('1'<=s[ni][nj]&&s[ni][nj]<='9'){
        nk=s[ni][nj]-'0';
      }
      if(d[ni][nj][nk]!=-1) continue;
      if('a'<=s[ni][nj]&&s[ni][nj]<='i'){
        if(s[ni][nj]-'a'+1==nk){
          d[ni][nj][nk]=d[i][j][k]+1;
          Q.push({ni,nj,nk});
        }
      }
      else{
        d[ni][nj][nk]=d[i][j][k]+1;
        Q.push({ni,nj,nk});
      }
    }
  }
  int ans=2e9;
  for(int i=0;i<=m;i++) if(d[gi][gj][i]!=-1) ans=min(ans,d[gi][gj][i]);
  if(ans>1e9) ans=-1;
  cout<<ans<<endl;
}