#include <bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define R cin>>
#define ll long long
#define ln cout<<'\n'
#define in(a) insert(a)
#define pb(a) push_back(a)
#define pd(a) printf("%.10f\n",a)
#define mem(a) memset(a,0,sizeof(a))
#define all(c) (c).begin(),(c).end()
#define iter(c) __typeof((c).begin())
#define rrep(i,n) for(ll i=(ll)(n)-1;i>=0;i--)
#define REP(i,m,n) for(ll i=(ll)(m);i<(ll)(n);i++)
#define rep(i,n) REP(i,0,n)
#define tr(it,c) for(iter(c) it=(c).begin();it!=(c).end();it++)
ll check(ll n,ll m,ll x,ll y){return x>=0&&x<n&&y>=0&&y<m;}void pr(){ln;}
template<class A,class...B>void pr(const A &a,const B&...b){cout<<a<<(sizeof...(b)?" ":"");pr(b...);}
template<class A>void PR(A a,ll n){rep(i,n)cout<<(i?" ":"")<<a[i];ln;}
const ll MAX=1e9+7,MAXL=1LL<<61,dx[8]={-1,0,1,0,-1,-1,1,1},dy[8]={0,1,0,-1,-1,1,1,-1};
typedef pair<ll,ll> P;
typedef pair<P,P> PP;

ll d[555][555][2],a[555][555];

void Main() {
  ll n,m;
  cin >> n >> m;
  rep(i,m) {
    ll x,y,z;
    cin >> x >> y >> z;
    x--,y--;
    a[x][y]=z;
  }
  priority_queue<PP,vector<PP>,greater<PP> > que;
  rep(i,n)rep(j,n)rep(k,2) d[i][j][k]=MAXL;
  d[0][0][0]=0;
  que.push(PP(P(0,0),P(0,0)));
  while(!que.empty()) {
    PP p=que.top();que.pop();
    ll x=p.S.F,y=p.S.S,c=p.F.F,k=p.F.S;
    if(d[x][y][k]<c) continue;
    rep(i,4) {
      ll xx=x+dx[i],yy=y+dy[i];
      if(check(n,n,xx,yy)) {
        ll cc=1;
        if(!k&&d[xx][yy][1]>c+cc) {
          d[xx][yy][1]=c+cc;
          que.push(PP(P(c+cc,1),P(xx,yy)));
        }
        cc=a[xx][yy]+1;
        if(d[xx][yy][k]>c+cc) {
          d[xx][yy][k]=c+cc;
          que.push(PP(P(c+cc,k),P(xx,yy)));
        }
      }
    }
  }
  pr(d[n-1][n-1][1]);
}

int main(){ios::sync_with_stdio(0);cin.tie(0);Main();return 0;}