#include <bits/stdc++.h>
using namespace std;
#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first
#define S second
typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PII;
typedef double db;
struct DSU
{
int n;
VI p, sz;
void init(int _n)
{
n = _n;
p.resize(n);
iota(ALL(p), 0);
sz.assign(n, 1);
}
int find(int v)
{
if (v == p[v])
return v;
return p[v] = find(p[v]);
}
bool unite(int u, int v)
{
u = find(u);
v = find(v);
if (u == v)
return false;
if (sz[u] > sz[v])
swap(u, v);
p[u] = v;
sz[v] += sz[u];
return true;
}
} d;
const int N = 147;
int n;
int deg[N];
int e[N][N];
int g[N][N];
int ng[N][N];
bool used[N];
bool dfs(int v, int p = -1)
{
used[v] = true;
if (p != -1 && (deg[v] & 1))
{
return true;
}
FOR (i, 0, n)
{
if (!used[i] && ng[v][i])
{
bool ok = dfs(i, v);
if (ok)
{
e[v][i] ^= 1;
e[i][v] ^= 1;
deg[v]++;
deg[i]++;
return true;
}
}
}
return false;
}
void solve()
{
vector<VI> comps(n);
FOR (i, 0, n)
{
comps[d.find(i)].PB(i);
//cerr << i << ' ' << d.find(i) << '\n';
}
VI odd;
FOR (i, 0, n)
{
auto& c = comps[i];
sort(ALL(c), [&](int u, int v)
{
return (deg[u] & 1) > (deg[v] & 1);
});
if (!c.empty() && deg[c[0]] & 1)
odd.PB(i);
}
//cerr << "Odd " << SZ(odd) << '\n';
vector<PII> ans;
if (SZ(odd) == 1)
{
int j = odd[0];
int v = -1;
FOR (i, 0, n)
if (d.find(i) != j)
v = i;
for (auto u : comps[j])
{
if (deg[u] & 1)
{
d.unite(u, v);
deg[u]++;
deg[v]++;
e[v][u]++;
e[u][v]++;
}
}
}
else
{
FOR (i, 0, SZ(odd))
{
int j = odd[i];
int v = comps[j][0];
int idx = odd[(i + 1) % SZ(odd)];
int k = 1;
while (k < SZ(comps[idx]) && deg[comps[idx][k]] & 1)
{
int u = comps[idx][k];
e[v][u]++;
e[u][v]++;
k++;
deg[v]++;
de
g[u]++;
//cerr << u << ' ' << v << '\n';
}
d.unite(comps[j][0], comps[idx][0]);
}
}
//FOR (i, 0, n)
// assert(deg[i] % 2 == 0);
comps.clear();
comps.resize(n);
FOR (i, 0, n)
{
comps[d.find(i)].PB(i);
}
VI idx;
FOR (i, 0, n)
{
if (comps[i].empty())
continue;
idx.PB(i);
}
if (SZ(idx) > 2)
{
FOR (i, 0, SZ(idx))
{
int j = (i + 1) % SZ(idx);
e[comps[idx[i]][0]][comps[idx[j]][0]]++;
e[comps[idx[j]][0]][comps[idx[i]][0]]++;
}
}
else if (SZ(idx) == 2)
{
if (SZ(comps[idx[0]]) >= 2 && SZ(comps[idx[1]]) >= 2)
{
FOR (i, 0, 2)
{
FOR (j, 0, 2)
{
int u = comps[idx[0]][i];
int v = comps[idx[1]][j];
e[u][v]++;
e[v][u]++;
}
}
}
else
{
if (SZ(comps[idx[0]]) != 1)
swap(idx[0], idx[1]);
int u = comps[idx[0]][0];
int v = -1;
int w = -1;
FOR (i, 0, SZ(comps[idx[1]]))
{
FOR (j, 0, i)
{
int x = comps[idx[1]][i];
int y = comps[idx[1]][j];
if (ng[x][y])
v = x, w = y;
}
}
if (v == -1)
{
cout << -1 << '\n';
return;
}
e[u][v] ^= 1;
e[v][u] ^= 1;
e[u][w] ^= 1;
e[v][w] ^= 1;
e[w][u] ^= 1;
e[w][v] ^= 1;
}
}
FOR (i, 0, n)
{
FOR (j, 0, i)
{
// cerr << i << ' ' << j << ' ' << e[i][j] << '\n';
if (e[i][j] & 1)
{
ans.PB({j, i});
}
}
}
cout << SZ(ans) << '\n';
for (auto [u, v] : ans)
cout << u + 1 << ' ' << v + 1 << '\n';
}
int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
int m;
cin >> n >> m;
d.init(n);
FOR (i, 0, m)
{
int u, v;
cin >> u >> v;
u--, v--;
d.unite(u, v);
g[u][v] = 1;
g[v][u] = 1;
deg[u]++;
deg[v]++;
}
FOR (i, 0, n) FOR (j, 0, n)
{
if (i == j)
continue;
ng[i][j] = 1 - g[i][j];
}
if (d.sz[d.find(0)] != n)
{
solve();
return 0;
}
FOR (i, 0, n)
{
if (deg[i] & 1)
{
if (!dfs(i))
{
cout << -1 << '\n';
return 0;
}
fill(used, used + n, false);
}
}
vector<PII> ans;
FOR (i, 0, n)
{
FOR (j, 0, i)
if (e[i][j] & 1)
ans.PB({j, i});
}
cout << SZ(ans) << '\n';
for (auto [u, v] : ans)
cout << u + 1 << ' ' << v + 1 << '\n';
return 0;
}