1 Program poj3159;
  2
  3 type cord=record
  4
  5              ne,da,po:longint;
  6
  7           end;
  8
  9
 10 var n,m,le,tot:longint;
 11
 12     head,dis:array[1..30000]of longint;
 13
 14     h,v:array[1..200000]of longint;
 15
 16     f:array[1..30000]of boolean;
 17
 18     link:array[1..200000]of cord;
 19
 20
 21   Procedure add(x,y,z:longint);
 22
 23    begin
 24
 25        inc(le);
 26
 27        with link[le] do
 28
 29          begin
 30
 31             po:=y;
 32
 33             da:=z;
 34
 35             ne:=head[x];
 36
 37          end;
 38
 39        head[x]:=le;
 40
 41    end;
 42
 43
 44   Procedure init;
 45
 46   var i,j,k,l:longint;
 47
 48    begin
 49
 50       readln(n,m);
 51
 52       for i:=1 to m do
 53
 54        begin
 55
 56           readln(j,k,l);
 57
 58           add(j,k,l);
 59
 60        end;
 61
 62    end;
 63
 64
 65   Procedure spfa(x:longint);
 66
 67   var i,j,k,t:longint;
 68
 69    begin
 70
 71       for i:=1 to n do dis[i]:=maxlongint div 3;
 72
 73       dis[x]:=0;
 74
 75       h[1]:=x;
 76
 77       f[x]:=true;
 78
 79       t:=1;
 80
 81       repeat
 82
 83          k:=h[t];
 84
 85          dec(t);
 86
 87          f[k]:=false;
 88
 89          i:=head[k];
 90
 91          while i<>0 do
 92
 93           begin
 94
 95              if dis[k]+link[i].da<dis[link[i].po] then
 96
 97                  begin
 98
 99                      dis[link[i].po]:=dis[k]+link[i].da;
100
101                      if f[link[i].po]=false then
102
103                         begin
104
105                             f[link[i].po]:=true;
106
107                             inc(t);
108
109                             h[t]:=link[i].po;
110
111                         end;
112
113                  end;
114
115              i:=link[i].ne;
116
117           end;
118
119
120       until  t=0;
121
122    end;
123
124
125   Procedure main;
126
127   var i,j:longint;
128
129    begin
130
131       spfa(1);
132
133       writeln(dis[n]);
134
135    end;
136
137
138 Begin
139
140
141
142          init;
143
144          main;
145
146
147
148 end.