#include<iostream> using namespace std; int n,m,f[105][105]; int map[105][105]; int sx[4]={-1,0,1,0},sy[4]={0,-1,0,1}; void dfs(int x,int y,int money,int color,bool mai){ if(money>=f[x][y])return ; f[x][y]=money; for(int i=0;i<=3;i++){ if(map[x+sx[i]][y+sy[i]]==0){ if(!mai)dfs(x+sx[i],y+sy[i],money+2,color,1);continue; }else{ if(map[x+sx[i]][y+sy[i]]==color) dfs(x+sx[i],y+sy[i],money,map[x+sx[i]][y+sy[i]],0); if(map[x+sx[i]][y+sy[i]]!=color) dfs(x+sx[i],y+sy[i],money+1,map[x+sx[i]][y+sy[i]],0); } } } int main(){ scanf("%d%d",&n,&m); for(int i=1;i<=n;i++) for(int j=1;j<=n;j++) f[i][j]=2e9; for(int i=1;i<=m;i++){ int x,y,color; scanf("%d%d%d",&x,&y,&color); map[x][y]=color+1; } dfs(1,1,0,map[1][1],0); if(f[n][n]==INT_MAX){printf("-1\n");return 0;} else printf("%d\n",f[n][n]); return 0; }