// Sooke bless me.
// LJC00118 bless me.
#include<bits/stdc++.h>

#define INF 2147483647
#define ll long long

int Inp(){
	char c = getchar();
	int Neg = 1;
	while(c < '0' || c > '9'){
		if(c == '-')
			Neg = -1;
		c = getchar();
	}
	int Sum = 0;
	while(c >= '0' && c <= '9'){
		Sum = ((Sum << 3) + (Sum << 1)) + c - '0';
		c = getchar();
	}
	return Neg * Sum;
}

int Head[50010], Next[400010], End[400010];
bool Used[50010];
int Ans[50010], Index = 0;
int Cou = 0;

void Link(int a, int b){
	Next[++Cou] = Head[a];
	Head[a] = Cou;
	End[Cou] = b;
}

bool Dfs(int Cur, int Edge){
	Used[Cur] = true;
	int Degree = 0;
	for(int x = Head[Cur]; x != -1; x = Next[x]){
		if(Used[End[x]])
			continue;
		if(Dfs(End[x], x))
			Degree++;
	}
	if(Degree % 2 == 1)
		return false;
	Ans[++Index] = (Edge + 1) >> 1;
	return true;
}

int main(){
	memset(Head, -1, sizeof(Head)); 
	int n = Inp();
	int m = Inp();
	for(int i = 1; i <= m; i++){
		int a = Inp();
		int b = Inp();
		Link(a, b);
		Link(b, a);
	}
	for(int i = 1; i <= n; i++)
		if(!Used[i])
			if(Dfs(i, -1)){
				printf("-1");
				return 0;
			}
	std::sort(Ans + 1, Ans + Index + 1);
	printf("%d", Index);
	for(int i = 1; i <= Index; i++)
		printf("\n%d", Ans[i]);
}