#include <cstdio>
#include <iostream>
#include <algorithm>
#include <set>
#include <map>
#include <stack>
#include <list>
#include <queue>
#include <deque>
#include <cctype>
#include <string>
#include <vector>
#include <sstream>
#include <iterator>
#include <numeric>
#include <cmath>
using namespace std;

typedef pair<int,int> PII;

#define ALL(x) x.begin(),x.end()
#define REP(i,n) for (int i=0; i<(n); ++i)
#define FOR(var,pocz,koniec) for (int var=(pocz); var<=(koniec); ++var)
#define FORD(var,pocz,koniec) for (int var=(pocz); var>=(koniec); --var)
#define PB push_back
#define PF push_front
#define MP(a,b) make_pair(a,b)
#define F first
#define S second
#define LD long double

#define MAX 300

vector<vector<int> > G;

vector<int> R;

inline void doFail(){
	printf("impossible\n");
	exit(0);
}

inline void doPut(int v, int d){
	if (R[v]==-d) doFail();
	R[v]=d;
}

pair<int,int> dfs(int v, int d){
	pair<int,int> r=MP(0,0);
	if (d==1) r.F++; else r.S++;
	doPut(v,d);
	REP(t,G[v].size()){
		int w=G[v][t];
		if (R[w]==0){
			pair<int,int> rw=dfs(w,-d);
			r.F+=rw.F; r.S+=rw.S;
		} else {
			if (R[w]==d) doFail(); 
		}
	}
	return r;
}

int main(){
	int n,m;

	int ret=0;

	scanf("%d%d",&n,&m);
	R=vector<int>(n,0);
	G=vector<vector<int> > (n,vector<int>());
	REP(i,m){
		int a,b,c;
		scanf("%d%d%d",&a,&b,&c);
        --a; --b;
		int d=c-1;
		if (d!=0){
			doPut(a,d);
			doPut(b,d);
		} else {
			G[a].PB(b);
			G[b].PB(a);
		}
	}
	REP(v,n) if (R[v]!=0) dfs(v,R[v]);

	REP(v,n) if (R[v]==1) ret++;

	REP(v,n) if (R[v]==0){
		pair<int,int> r = dfs(v,-1);
		ret+=min(r.F,r.S);
	}
	printf("%d\n",ret);

	return 0;
}