#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <cctype>

#include <iostream>
#include <sstream>
#include <string>

#include <vector>
#include <list>
#include <queue>
#include <set>
#include <map>
#include <stack>
#include <algorithm>
using namespace std;

#define FOR(i,n) for(int i=0; i < (n); i++)
#define FORD(i,n) for(int i=(n)-1; i >= 0; i--)
#define FORTO(i,a,b) for (int i = (a); i <= (b); ++i)

#define DEBUG(x) cout << '>' << #x << ' ' << x << endl;
#define SIZE(x) int(x.size())

typedef pair<int, int> PII;
typedef long long ll;

#define MAXN 10047

vector<int> Adj[MAXN];

bool V[MAXN]; // visited
bool B[MAXN]; // broken

set<PII> R;

bool DFS(int v) {
	if (V[v]) return false;
	V[v] = true;
	FOR(i,SIZE(Adj[v])) {
		int u = Adj[v][i];
		if (!V[u]) {
			bool r = DFS(u);
			B[v] ^= r;
			if (r) R.insert(PII(v,u));
		}
	}
	return B[v];
}

char S[MAXN];

int main() {
	
	while (true) {
		int N, M;
		scanf("%d %d", &N, &M);
		if (!N) return 0;
		
		FORTO(i,1,N) {
			Adj[i].clear();
			V[i] = false;
			B[i] = false;
		}
		R.clear();
		
		vector<PII> X;
		
		FOR(i,M) {
			int a, b;
			scanf("%d %d", &a, &b);
			X.push_back(PII(a,b));
			Adj[a].push_back(b);
			Adj[b].push_back(a);
		}
		
		scanf(" %s", S);
		
		FORTO(i,1,N) {
			if (S[i-1] == 'e' && SIZE(Adj[i])%2 == 1) B[i] = true;
			if (S[i-1] == 'o' && SIZE(Adj[i])%2 == 0) B[i] = true;
		}
		
		bool ok = true;
		
		FORTO(i,1,N) if (DFS(i)) ok = false;
		
		if (!ok) {
			printf("impossible\n");
		} else {
			printf("%d\n", M-SIZE(R));
			FOR(i,M) {
				PII back = PII(X[i].second,X[i].first);
				if (!R.count(X[i]) && !R.count(back))
					printf("%d %d\n", X[i].first, X[i].second);
			}
		}
	}
	return 0;
}