#include <bits/stdc++.h>
using namespace std;
int n, m, X, Y, tp, cnt, k[200010], a[200010][2], pos[200010][2], stk[400010], ans[300010][2];
bool bk[200010];
void chg(int x, int y){
	cnt++; ans[cnt][0] = x; ans[cnt][1] = y;
	if(X == y){ X = Y; Y = 0; }
	else if(Y == y) Y = 0;
	int i = a[x][--k[x]];
	if(pos[i][0] == x) pos[i][0] = y;
	else pos[i][1] = y;
	a[y][k[y]++] = i;
	if(k[x] > 0) stk[++tp] = a[x][k[x] - 1];
	else if(X == 0) X = x;
	else if(Y == 0) Y = x;
}
void upd(){
	int i, x, y;
	while(tp > 0){
		i = stk[tp--]; x = pos[i][0]; y = pos[i][1];
		if(x == y || i != a[x][k[x] - 1] || i != a[y][k[y] - 1]) continue;
		if(k[x] == 1) chg(y, x);
		else if(k[y] == 1) chg(x, y);
	}
}
void dfs1(int u, int fa){
	int x = pos[u][0] + pos[u][1] - fa;
	bool fl = (a[fa][k[fa] - 1] == u && a[x][k[x] - 1] == u);
	if(k[x] > 1) dfs1(a[x][0] + a[x][1] - u, x);
	if(fl){
		int tmp = X;
		chg(fa, tmp); chg(x, tmp); upd();
	}
}
void dfs2(int u, int fa, int rt, int &p){
	int x = pos[u][0] + pos[u][1] - fa;
	if(a[fa][1] == u && a[x][1] == u){
		if(p == 0) p = u;
		else p = -1;
	}
	if(x != rt) dfs2(a[x][0] + a[x][1] - u, x, rt, p);
}
void dfs3(int u, int fa, int rt){
	bk[fa] = true;
	int x = pos[u][0] + pos[u][1] - fa;
	if(x != rt) dfs3(a[x][0] + a[x][1] - u, x, rt);
}
void dfs4(int u, int fa, int rt){
	int x = pos[u][0] + pos[u][1] - fa;
	bool fl = (a[fa][1] == u && a[x][1] == u);
	if(x != rt) dfs4(a[x][0] + a[x][1] - u, x, rt);
	if(fl){
		int tmp = X;
		chg(fa, tmp); chg(x, tmp); upd();
	}
}
void solve(){
	X = 0; Y = 0; tp = 0; cnt = 0;
	int i, j, tmp;
	for(i = 1; i <= n; i++) pos[i][0] = 0;
	for(i = 1; i <= m; i++){
		scanf("%d", &k[i]);
		for(j = 0; j < k[i]; j++){
			scanf("%d", &a[i][j]);
			if(pos[a[i][j]][0] == 0) pos[a[i][j]][0] = i;
			else pos[a[i][j]][1] = i;
		}
		if(k[i] > 0) stk[++tp] = a[i][k[i] - 1];
		else if(X == 0) X = i;
		else if(Y == 0) Y = i;
		bk[i] = false;
	}
	upd();
	if(X != 0){
		for(i = 1; i <= m; i++){
			if(k[i] == 1) dfs1(a[i][k[i] - 1], i);
		}
		for(i = 1; i <= m; i++){
			if(k[i] == 2 && !bk[i] && a[i][0] != a[i][1]){
				j = 0; dfs2(a[i][0], i, i, j);
				if(j == 0){
					chg(i, X); upd();
				}else if(j > 0){
					tmp = X; chg(pos[j][0], tmp); chg(pos[j][1], tmp); upd();
				}else dfs3(a[i][0], i, i);
			}
		}
		if(Y != 0){
			for(i = 1; i <= m; i++){
				if(k[i] == 2 && bk[i] && a[i][0] != a[i][1]){
					dfs4(a[i][0], i, i);
				}
			}
		}
	}
	for(i = 1; i <= n; i++){
		if(pos[i][0] != pos[i][1]){ printf("-1\n"); return; }
	}
	printf("%d\n", cnt);
	for(i = 1; i <= cnt; i++) printf("%d %d\n", ans[i][0], ans[i][1]);
}
int main()
{
	while(~scanf("%d%d", &n, &m)){
		solve();
	}
	return 0;
}