#include<iostream>
#include<algorithm>
#include<cstring>
using namespace std;
const int N=510,M=100010;

struct Edge
{
    int a,b,c;
}edges[M];

int n,m,k;
int dist[N];
int last[N];

void bellman_ford()
{
    memset(dist,0x3f,sizeof dist);
    dist[1]=0;
    for(int i=0;i<k;i++)
    {
        memcpy(last,dist,sizeof dist); //last拷贝dist,防止存在负环更改自己的值不能影响之前存在的值.
        for(int j=0;j<m;++j)
        {
            auto e=edges[j];
            dist[e.b]=min(dist[e.b],last[e.a]+e.c);
        }
    }
}
int main()
{
    scanf("%d%d%d",&n,&m,&k);
    for(int i=0;i<m;++i)
    {
        int a,b,c;
        scanf("%d%d%d",&a,&b,&c);
        edges[i]={a,b,c};
    }
    bellman_ford();
    if(dist[n]>0x3f3f3f3f/2) puts("impossible");
    else cout<<dist[n];
    return 0;
}