#pragma GCC optimize("Ofast")
	#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,fma,abm,mmx,avx,tune=native")
	#include <bits/stdc++.h>
	#include <ext/pb_ds/assoc_container.hpp> // Common file  
	#include <ext/pb_ds/tree_policy.hpp>  
	#include <functional> // for less  
	#include <iostream>  
	using namespace __gnu_pbds;  
	using namespace std;
	#define ll long long
	typedef tree<pair<ll,ll>, null_type, less<pair<ll,ll>>, rb_tree_tag,tree_order_statistics_node_update>  ordered_set;
	using namespace std;
	 
	#define fr(i,a,b) for (int i = (a), _b = (b); i <= _b; i++)
	#define frr(i,a,b) for (int i = (a), _b = (b); i >= _b; i--)
	#define rep(i,n) for (long long i = 0, _n = (n); i < _n; i++)
	#define repr(i,n) for (long long i = (n) - 1; i >= 0; i--)
	#define foreach(it,ar) for ( typeof(ar.begin()) it = ar.begin(); it != ar.end(); it++ )
	#define fill(ar,val) memset(ar, val, sizeof(ar))
	#define fill0(ar) fill((ar), 0)
	#define fillinf(ar, n) fr(i,0,(n)) ar[i] = INF
	#define debug(x) cout<<#x<<": "<<x<<endl
	#define arr1d(a,n) cout << #a << " : "; fr(_,1,n) cout << a[_] << ' '; cout << endl;
	#define arr1d0(a,n) cout << #a << " : "; rep(_,n) cout << a[_] << ' '; cout << endl;
	#define arr2d(a,n,m) cout << #a << " :" << endl; fr(_,1,n) {fr(__,1,m) cout << a[_][__] << ' '; cout << endl;}
	#define arr2d0(a,n,m) cout << #a << " :" << endl; rep(_,n) {rep(__,m) cout << a[_][__] << ' '; cout << endl;}
	/*Author Ritick Goenka || ritick(codechef) ||ritick(codeforces) */
	/*IIT Roorkee = <3 */
	#define ull unsigned long long
	#define ld long double
	#define ui unsigned int
	#define all(ar) ar.begin(), ar.end()
	#define pb push_back
	#define mp make_pair
	#define ff first
	#define ss second
	#define y0 yyyyyy0
	auto clk=clock();
	#define y1 yyyyyy1
	#define setb __builtin_popcount
	#define BIT(n) (1<<(n))
	#define SQR(x) ((x) * (x))
	#define CUBE(x) ((x) * (x) * (x))
	#define LSOne(S) (S) & (-S)
	inline bool EQ(double a, double b) {return fabs(a - b) < 1e-9;}
	 
	typedef pair<int, int> ii;
	typedef pair<int, ii> iii;
	typedef vector<ii> vii;
	typedef vector<int> vi;
	typedef vector<string> vs;
	 
	template<typename T>inline T gcd(T a, T b){if (b == 0)return a;else return gcd(b, a % b);}
	// template<typename T>inline T lcm(T a, T b){return (a * b) / gcd(a, b);}
	template<typename T> string toStr(T x) {stringstream st; st << x; string s; st >> s; return s;}
	template<class T>
	void splitStr(const string &s, vector<T> &out)
	{
	    istringstream in(s);
	    out.clear();
	    copy(istream_iterator<T>(in), istream_iterator<T>(), back_inserter(out));
	}
	 
	inline int two(int n) {return 1 << n;}
	inline int isOnBit(int n, int b) {return (n >> b) & 1;}
	inline void onBit(int & n, int b) {n |= two(b);}
	inline void offBit(int & n, int b) {n &= ~two(b);}
	inline int lastBit(int n) {return n & (-n);}
	inline int cntBit(int n) {int res = 0; while(n && ++res) n -= n &(-n); return res;}
	 
	const int dx4[] = {-1, 0, 1, 0};
	const int dy4[] = {0, 1, 0, -1};
	const int dx8[] = {-1, 0, 1, 0, -1, -1, 1, 1};
	const int dy8[] = {0, 1, 0, -1, -1, 1, -1, 1};
	 
	#define INP "test.inp"
	#define OUT "test.out"
	 
	#define PI 3.1415926535897932385
	#define INF 10000000000000000ll
	#define EPS 1e-7
	#define MAXN 100000
	#define MOD 1000000007
	#define dec decr
	#define endl '\n'
	 
	mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
	ll gcd(ll a, ll b) 
	{ 
	    if (a == 0) 
	        return b; 
	    return gcd(b % a, a); 
	} 
	ll modexp(ll x, ll y, ll p)
	{
	    ll res = 1;   
	    x = x % p;  
	    while (y > 0)
	    {
	        if (y %2==1)    
	            res = (res*x) % p;
	        y = y>>1;     
	        x = (x*x) % p; 
	    }
	    return res;
	}
	 ll find(ll x,ll y,ll z)
	 {
	 	ll n=x;
	 	if(x%z!=0)
	 		n=x+(z-x%z);
	 	if(n>y)
	 		return 0;
	 	ll ans=1;
	 	ll p=y-n;
	 	return p/z+1;
	 }
	 ll mat[105][105];
	int main () 
	{
	    ios_base::sync_with_stdio(false);
	    cin.tie(NULL);
	    cout<<fixed;
	    cout<<setprecision(9);
	    #ifdef rg
	    freopen("input.txt", "r", stdin);
	    freopen("output.txt", "w", stdout);
	    #endif
	    ll n,m;
	    cin>>n>>m;
	    ll zz=(n-1)*(n-2)/2;
	    if(m>zz)
	    {
	    	cout<<"-1";
	    	return 0;
	    }
	    rep(i,n)
	    {
	    	rep(j,n)
	    	if(i!=j)
	    	mat[i+1][j+1]=1;
	    }
	    ll z=n-2;
	    ll ans=n*(n-1)/2;
	    ans-=m;
	    for(ll i=2;i<=n;i++)
	    {
	    	if(m>z)
	    	{
	    		m-=z;
	    		for(ll j=2;j<=n;j++)
	    		{
	    			mat[i][j]=0;
	    			mat[j][i]=0;
	    		}
	    	}
	    	else
	    	{
	    		ll x=m;
	    		m-=x;
	    		for(ll j=2;j<=n;j++)
	    		{
	    			if(mat[i][j]==1)
	    			{
	    				x--;
	    				mat[i][j]=0;
	    				mat[j][i]=0;

	    			}
	    			if(x==0)
	    				break;
	    		}
	    	}
	    	// debug(m);
	    	if(m==0)
	    		break;
	    	z--;
	    }
	    cout<<ans<<endl;
	    for(ll i=1;i<=n;i++)
	    {
	    	for(ll j=1;j<=n;j++)
	    	{
	    		if(mat[i][j])
	    		{
	    			cout<<i<<' '<<j<<endl;
	    			mat[i][j]=0;
	    			mat[j][i]=0;
	    		}
	    	}
	    }

	    #ifdef rg
	    cout<<endl<<endl<<"Time elapsed: "<<(double)(clock()-clk)/CLOCKS_PER_SEC<<endl;
	    #endif
	    return 0;
	}   

Measured memory_bytes: 384