#ifdef LOCAL
//#define _GLIBCXX_DEBUG
#endif
//#pragma GCC target("avx512f,avx512dq,avx512cd,avx512bw,avx512vl")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<ll, ll> P;
typedef pair<int, int> Pi;
typedef vector<ll> Vec;
typedef vector<int> Vi;
typedef vector<string> Vs;
typedef vector<char> Vc;
typedef vector<P> VP;
typedef vector<vector<ll>> VV;
typedef vector<vector<int>> VVi;
typedef vector<vector<char>> VVc;
typedef vector<vector<vector<ll>>> VVV;
typedef vector<vector<vector<vector<ll>>>> VVVV;

#define endl '\n'
#define REP(i, a, b) for(ll i=(a); i<(b); i++)
#define PER(i, a, b) for(ll i=(a); i>=(b); i--)
#define rep(i, n) REP(i, 0, n)
#define per(i, n) PER(i, n, 0)
const ll INF=1e18+18;
const ll MOD=1000000007;
#define Yes(n) cout << ((n) ? "Yes" : "No") << endl;
#define YES(n) cout << ((n) ? "YES" : "NO") << endl;
#define ALL(v) v.begin(), v.end()
#define rALL(v) v.rbegin(), v.rend()
#define pb(x) push_back(x)
#define mp(a, b) make_pair(a,b)
#define Each(a,b) for(auto &a :b)
#define rEach(i, mp) for (auto i = mp.rbegin(); i != mp.rend(); ++i)
#ifdef LOCAL
#define dbg(x_) cerr << #x_ << ":" << x_ << endl;
#define dbgmap(mp) cerr << #mp << ":"<<endl; for (auto i = mp.begin(); i != mp.end(); ++i) { cerr << i->first <<":"<<i->second << endl;}
#define dbgset(st) cerr << #st << ":"<<endl; for (auto i = st.begin(); i != st.end(); ++i) { cerr << *i <<" ";}cerr<<endl;
#define dbgarr(n,m,arr) rep(i,n){rep(j,m){cerr<<arr[i][j]<<" ";}cerr<<endl;}
#define dbgdp(n,arr) rep(i,n){cerr<<arr[i]<<" ";}cerr<<endl;
#else
#define dbg(...)
#define dbgmap(...)
#define dbgset(...)
#define dbgarr(...)
#define dbgdp(...)
#endif
#define out(a) cout<<a<<endl
#define out2(a,b) cout<<a<<" "<<b<<endl
#define vout(v) rep(i,v.size()){cout<<v[i]<<" ";}cout<<endl
#define Uniq(v) v.erase(unique(v.begin(), v.end()), v.end())
#define fi first
#define se second

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; }

template<typename T1, typename T2>
ostream &operator<<(ostream &s, const pair<T1, T2> &p) { return s<<"("<<p.first<<", "<<p.second<<")"; }

template<typename T>istream& operator>>(istream&i,vector<T>&v)
{rep(j,v.size())i>>v[j];return i;}

// vector
template<typename T>
ostream &operator<<(ostream &s, const vector<T> &v) {
    int len=v.size();
    for(int i=0; i<len; ++i) {
        s<<v[i];
        if(i<len-1) s<<"	";
    }
    return s;
}

// 2 dimentional vector
template<typename T>
ostream &operator<<(ostream &s, const vector<vector<T> > &vv) {
    s<<endl;
    int len=vv.size();
    for(int i=0; i<len; ++i) {
        s<<vv[i]<<endl;
    }
    return s;
}

int solve(){
    ll x,y;
    cin>>x>>y;
    Yes(abs(x-y)<3);
    return  0;
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout<<std::setprecision(10);
//    ll T;
//    cin>>T;
//    while(T--)
    solve();
}

#include<iostream>
#include<algorithm>
#include<string>
#include<map>
#include<iomanip>
#include<vector>
#include<queue>
//#include<atcoder/segtree>
#define rep(i, n) for(int i=0; i<n; i++)
using namespace std;
typedef long long ll;
using P = pair<int,int>;
using T = tuple<int,int,int>;
const int INF = 1e9;
//using namespace atcoder;

int main(){
    int h, w; cin >> h >> w;
    vector<vector<P> > alp(30);
    string a[h];
    P s, g;
    int cost[h][w];
    queue<P> q;
    rep(i,h) cin >> a[i];
    rep(i,h)rep(j,w){
        if(a[i][j]=='S'){ s.first=i; s.second=j;}
        else if(a[i][j]=='G'){
            //P g(i,j);
            g.first=i; g.second=j;
            }
        else if(a[i][j]=='#') cost[i][j]=-2;
        else if(a[i][j]=='.') continue;
        else{
            alp[a[i][j]-'a'].push_back(P(i,j));
        }
    }
    rep(i,h)rep(j,w) cost[i][j]=-1;
    
    P tmp;
    q.push(s);
    cost[s.first][s.second] = 0;
    int already[30]={};
    while(!q.empty()){
        tmp = q.front(); q.pop();
        int x = tmp.first, y = tmp.second;
        if(x>0){
            if(cost[x-1][y]==-1){
                if(a[x-1][y]!='#'){
                    cost[x-1][y] = cost[x][y]+1;
                    q.push(P(x-1,y));
                    }
            }
        }
        if(x<h-1){
            if(cost[x+1][y]==-1){
                if(a[x+1][y]!='#'){
                    cost[x+1][y] = cost[x][y]+1;
                    q.push(P(x+1,y));
                    }
            }
        }
        if(y>0){
            if(cost[x][y-1]==-1){
                if(a[x][y-1]!='#'){
                    cost[x][y-1] = cost[x][y]+1;
                    q.push(P(x,y-1));
                    }
            }
        }
        if(y<w-1){
            if(cost[x][y+1]==-1){
                if(a[x][y+1]!='#'){
                    cost[x][y+1] = cost[x][y]+1;
                    q.push(P(x,y+1));
                    }
            }
        }
        if(a[x][y]!='S' && a[x][y]!='.' && a[x][y]!='#' && a[x][y]!='G'){
            if(already[a[x][y]-'a']==0){
                already[a[x][y]-'a']=1;
                rep(i, alp[a[x][y]-'a'].size()){
                    P teleport = alp[a[x][y]-'a'][i];
                    if(cost[teleport.first][teleport.second]==-1){
                        cost[teleport.first][teleport.second] = cost[x][y]+1;
                        q.push(P(teleport.first,teleport.second));
                    }
                }
            }
        }
    }
    //cout <<g.first<<" " <<g.second << endl;
    cout << cost[g.first][g.second] << endl;
}