#include <bits/stdc++.h>
using namespace std;
#define _ <<" "<<
#define sz(x) ((int) (x).size())
typedef pair<int, int> pii;
typedef long long ll;
const int maxn = 5e5 + 5;


int n, m;
vector<int> G[maxn];
int id[maxn];

void addedge(int a,int b) {
    G[a].push_back(b);
    G[b].push_back(a);
}

vector<pii> ans;

void dfs(int x,int fa) {
    for (auto v : G[x]) if (v != fa) {
        dfs(v, x);
        ans.push_back({v, x});
    }
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int a; cin >> a;
    char c; cin >> c;
    int b; cin >> b;
    int t = a*b;
    int n = b*b;
    if (a < b-1) {
        cout << "impossible\n";
        return 0;
    }
    if (a == b-1) {
        n = b;
        t = a;
    }
    int k = n;
    int maxdep = 0;
    id[0] = n; k--;
    int mx = n;

    // cout << "Tar" _ t _ k << endl;

    while (k <= t-maxdep) {
        addedge(k,mx); mx = k;
        id[++maxdep] = k;
        k--; 
        t -= maxdep;
    }
    //  cout << "Tar" _ t _ k << endl;
    for (int i = 1;i < k; ++i) {
        addedge(n, i);
        t--;
    }
    // cout << "Tar" _ t _ k << endl;
    addedge(id[t-1], k);
    dfs(n,0);
    cout << n _ n-1 << '\n';
    for (auto [a,b] : ans) {
        cout << a _ b << '\n';
    }
    return 0;
}