//#pragma comment(linker, "/stack:247474112")
// #pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native") 
#pragma GCC optimize("unroll-loops")

#include <bits/stdc++.h>
using namespace std;

// #include <ext/pb_ds/assoc_container.hpp> 
// #include <ext/pb_ds/tree_policy.hpp> 
// using namespace __gnu_pbds; 
  
//typedef tree<
//        pair<int, int>, // change type
//        null_type,
//        less<pair<int, int> >, // change type
//        rb_tree_tag,
//        tree_order_statistics_node_update>
//        ordered_set;

#define     pii             pair<int ,int>
#define     ff              first
#define     ss              second
#define     pb(x)           push_back(x ) 
#define     mp              make_pair
#define     pbxy(x,y )      push_back(make_pair(x,y ) )    
#define     sz(x)           x.size()
#define     clr(x)          x.clear()
#define     mem(x ,y)       memset(x , y , sizeof x )
#define     all(a )         a.begin() , a.end()
#define     endl            "\n"
#define     si(x )          scanf("%d", &x)
#define     sii(x,y )       scanf("%d%d", &x,&y)
#define     siii(x,y ,z)    scanf("%d%d%d ", &x,&y , &z)
#define     rep(i ,n )      for( __typeof(n) i = 0 ; i < n ; i++ )
#define     repi(i ,n )     for( __typeof(n) i = 1 ; i <= n ; i++ )
#define     forn(i ,x,n )   for( __typeof(n) i = x ; i <= n ; i++ )
#define     repit(i, c)     for( __typeof((c).begin()) i = (c).begin(); i != (c).end();++i )
#define     dbg(args...)    do {   cerr << #args << ' ' ;  print(args); } while(0); cerr<< endl ;
  
typedef long long ll  ;
typedef unsigned long long  ull ;
typedef vector<int> vi  ;

const int  mod =  1e6 +7;
const ll  inf = 1e15  ;
const long long  infL = 1e18 ;

int setbit(int n, int pos  ) { return n = n|(1<< pos) ; }
int resetbit(int n,int pos ) {  return n =  n & ~(1<<pos ); }
bool checkbit(int  n,int pos ) { return (bool ) (n&(1<<pos))  ; }

template < typename T > T mul(T x, T y   ) { x %= mod ; y %= mod ; return (x*y)%mod  ;  }
template < typename T > T add(T x, T y  ) { x %= mod ; y %= mod ; return (x+y)%mod ;  }
template < typename T > T modPow(T x, T k ,T mod ) { if(k == 0 ) return 1; if(k&1  ) { return ( (x%mod)*modPow(x,k-1, mod )%mod )%mod ; } else { T ret = modPow(x,k/2 , mod ) ; ret %= mod ; return (ret*ret )%mod; } }
template < typename T > T ext_gcd(T num1 , T num2, T &X , T &Y ) { T r2,r1, q2, q1 , x2, x1, y2 ,y1 , x,  y, r   ; x2 = 1; y2 = 0;  x1 = 0; y1 = 1; for( r2 =num1 ,r1 = num2 ;r1 != 0 ; y2 = y1, y1 = y,x2 = x1 ,x1 = x ,r2 = r1, r1 = r) {q1 = r2/r1; x = x2 - q1*x1; y = y2 - q1*y1; r = r2%r1 ; } X = x2 ; Y = y2 ; return r2 ;  }
template < typename T > T modInv( T x , T m ) {  return modPow(x,m-2 , m) ; }  // long long ret, t ;// ext_gcd( x, m ,ret ,t  ) ;// ret %= m ;// if(ret<0) ret += m  ; // return ret;}
template < typename T > void print(const T& v) {    cerr << v << ' ' ;}
template < typename T1, typename... T2 > void print( const T1& first, const T2&... rest ){ print(first); print(rest...) ;}
// debuging ... 
template < typename F, typename S >
ostream& operator << ( ostream& os, const pair< F, S > & p ) {
    return os << "[ " << p.first << ", " << p.second << " ]";
}

template < typename T >
ostream &operator << ( ostream & os, const vector< T > &v ) {
    os << "[ "; rep(i , sz( v)  )  os << v[i] << ' ' ; return os << " ]" ; 
}

//int dx[] = {0 , 0 ,+1, -1 } ;
//int dy[] = {-1, +1,0 , 0 };
  
const int M = (int )1e6+77 ;  
const int mx = (int)700; 
const int N = 1000 ;

////  code from here ... 

pair<ll,ll> a[M+2 ] ;
string s1,s2; 
int dp[N+2][N+2 ] ,cnt[N+2 ][N+2] ;
int last1[N+2][N+2] , last2[N +2][N+2]  ; 
int len  ;

int func(int i,int j ) {
    if(i>=sz(s1) or j>=sz(s2) ) return 0; 
    int &ans =dp[i][j]  ; 
    if(ans!=-1) return ans ;
    ans = 0; 
    if(s1[i]== s2[j] ) {
        ans = func( i+1, j+1) + 1 ; 
    } else {
        ans = max(func(i+1,j) , func(i,j+1 ) )  ; 
    }


    return ans ;
}

int func2(int i,int j ) {
    if(i>=sz(s1) or j>=sz(s2) ) return 0; 
    int &ans =cnt[i][j]  ; 
    if(ans!=-1) return ans ;
    ans = 0; 
    if(s1[i]== s2[j] ) {
        ans = func2( i+1, j+1) + (func(i,j)==len?1:0  ) ; 
        ans %= mod ;    
    } else {
        ans = add(func2(i+1,j) , func2(i,j+1 ) )   ; 
    }


    return ans ;
}

vector< pii >v; 
int ncr(int x   ) {
    return (x*(x-1))/2 ;
}
void  solve() {   
    int n,k ,cnt =2 , x  ,tot =0  ; cin >> n >> k ; 
    if( k > ncr(n-1) ) {
        cout<< "-1" ;return  ; 
    }
    tot = ncr(n-1)   ; 

    forn(i, 2,n ) v.pb(mp(1,i ) ) ; 



    forn(i,2,n ) {
        int f =1; 
        forn(j, i+1,n ) {
            if(tot== k){
                f=0 ; 
                break ; 
            } 
            tot-- ;
            v.pb(mp(i,j ) ) ; 
        }

        if(tot == k ) f = 0; 
        if(f==0 ) break ; 

    }






    cout << sz(v) << endl; 
    rep(i, sz(v) )  {

        cout <<v[i].ff << ' ' << v[i].ss <<endl;
    }



} 

int main() {
    
 
    int t=1 , c= 0 ;  //si( t) ;
   // clock_t s = clock()    ;
    ///cin >>t ; 
    while(t--) {
       // printf("Case %d: ",++c)  ;
        solve() ;
    }
    // double e  = (clock() -s )/(CLOCKS_PER_SEC*1.0 )  ;  
    // cerr << "exec time : " <<  e << endl ;; 

}





Measured memory_bytes: 2432