#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000005
#define Inf64 4000000000000000001LL

int main(){
	
	int h,w,m;
	cin>>h>>w>>m;
	vector<string> s(h);
	rep(i,h)cin>>s[i];
	
	int sx,sy,gx,gy;
	rep(i,h){
		rep(j,w){
			if(s[i][j]=='S'){
				sx = i,sy = j;
			}
			if(s[i][j]=='G'){
				gx = i,gy = j;
			}
		}
	}
	vector d(h,vector(w,vector<int>(m+1,Inf32)));
	queue<vector<int>> Q;
	Q.push({sx,sy,m});
	d[sx][sy][m] = 0;
	while(Q.size()>0){
		int x = Q.front()[0];
		int y = Q.front()[1];
		int k = Q.front()[2];
		Q.pop();
		vector<int> dx = {1,-1,0,0},dy= {0,0,1,-1};
		rep(i,4){
			int nx = x + dx[i],ny = y + dy[i];
			int nk = k;
			if(nx<0 || nx>=h || ny<0 || ny>=w) continue;
			if(s[nx][ny]=='#') continue;
			if(isdigit(s[nx][ny])){
				nk = (s[nx][ny]-'1');
			}
			else if(islower(s[nx][ny])){
				if(s[nx][ny]-'a'!=k)continue;
			}
			if(d[nx][ny][nk] <= d[x][y][k]+1) continue;
			d[nx][ny][nk] = d[x][y][k] + 1;
			Q.push({nx,ny,nk});
		}
	}
	int ans = Inf32;
	rep(i,m+1){
		ans = min(ans, d[gx][gy][i]);
	}
	if(ans == Inf32) ans = -1;
	cout<<ans<<endl;
	
	return 0;
}