#include<iostream>
#include<cstring>
#include<cstdlib>
#include<cstdio>
#include<bitset>
#include<algorithm>
#include<cmath>
using namespace std;
const int maxn=160, inf=1e9+160;
struct mtx{bitset<maxn>mp[maxn]; mtx(){for(int i=0;i<maxn;i++) mp[i].reset();}}tmp, tmp2, f, base, h[35];
struct poi{int x, y, dis;}a[maxn];
int n, m;
mtx operator *(mtx a, mtx b)
{mtx c;for(int i=1;i<=n;i++)for(int j=1;j<=n;j++)if(a.mp[i][j]) c.mp[i]|=b.mp[j];return c;
}
mtx operator |(mtx a, mtx b)
{mtx c; for(int i=1;i<=n;i++)c.mp[i]|=a.mp[i]|b.mp[i];return c;
}
inline void power(int b)
{if(b<=0) return;for(;b;b>>=1, tmp=tmp*tmp)if(b&1) f=f*tmp;
}
inline bool cmp(poi a, poi b){return a.dis<b.dis;}
int main()
{scanf("%d%d", &n, &m);for(int i=1;i<=m;i++) scanf("%d%d%d", &a[i].x, &a[i].y, &a[i].dis);sort(a+1, a+1+m, cmp); a[m+1].dis=inf;if(a[1].dis) return puts("Impossible"), 0;for(int i=1;i<=n;i++) f.mp[i][i]=1;for(int i=1;i<=m;i++){tmp=base; power(a[i].dis-a[i-1].dis);base.mp[a[i].x][a[i].y]=1;int up=log2(a[i+1].dis-a[i].dis);h[0]=base; for(int j=1;j<=n;j++) h[0].mp[j][j]=h[0].mp[j][j]|1;mtx tmpx; for(int j=1;j<=n;j++) tmpx.mp[j][j]=1;if(a[i+1].dis-a[i].dis & 1) tmpx=tmpx|(tmpx*h[0]);for(int j=1;j<=up;j++) {h[j]=h[j-1]*h[j-1];if(a[i+1].dis-a[i].dis & (1<<j)) tmpx=tmpx|(tmpx*h[j]);}tmpx=f*tmpx; if(!tmpx.mp[1][n]) continue;mtx tmp1=f; int ans=0;for(int j=up;j>=0;j--)if(a[i].dis+ans+(1<<j)<=a[i+1].dis){tmp2=tmp1; tmp2=tmp2*h[j];if(tmp2.mp[1][n]) continue;ans+=(1<<j); tmp1=tmp2;}return printf("%d\n", a[i].dis+ans+1), 0;}puts("Impossible");
}