#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;

#define INF 0x3f3f3f3f
const int N=505;
const int M=1e4+5;
int n, m, k;
int DIS[N];
int BACK[N]; // 路径备份, 阻止结果覆盖

struct EDGE{
    int x;
    int y;
    int w;
}edges[M];

int bellmanFord(){
    // 最多经过k条边
    DIS[1]=0;
    for(int i=0; i<k; ++i){
        memcpy(BACK, DIS, sizeof DIS);
        for(int j=m-1; j>=0; --j){
            int x=edges[j].x;
            int y=edges[j].y;
            int w=edges[j].w;
            DIS[y]=min(DIS[y], BACK[x]+w);
        }
    }
    if(DIS[n]>INF/2) return -1;
    return DIS[n];
}

int main(){
    memset(DIS, 0x3f, sizeof DIS);
    cin>>n>>m>>k;
    int x, y, w;
    for(int i=0; i<m; ++i){
        cin>>x>>y>>w;
        edges[i]={x, y, w};
    }
    int res=bellmanFord();
    if(res==-1) cout<<"impossible"<<endl;
    else cout<<res<<endl;

    return 0;
}