#include <iostream>
#include <cstdio>
#include <iostream>
#include <algorithm>
#include <iomanip>
#include <string>
#include <cassert>
#include <vector>
#include <cstring>
#include <queue>
using namespace std;

#define mp make_pair
#define pb push_back
#define all(v) (v).begin(), (v).end()
#define sz(v) (int)(v).size()
typedef long long LL;
typedef long double LD;

const int N = 2000007;
LL s[4200007], add[4200007];
LD f[4200007];
struct segtree
{
    inline LL gets(int v, int tl, int tr)
    {
        return s[v] + (tr - tl + 1) * add[v];
    }

    inline LD getf(int v, int tl, int tr)
    {
        LL k = add[v];
        if (k == 0) return f[v];
        if (k < 0)
        {
            k = -k;
            LD ret = f[v];
            ret -= gets(v, tl, tr) * k;
            ret -= (tr - tl + 1) * (LD)k * (k - 1) / 2.0;
            return ret;
        }
        LD ret = f[v];
        ret += s[v] * k;
        ret += (tr - tl + 1) * (LD)k * (k - 1) / 2.0;
        return ret;
    }

    void push(int v, int tl, int tr)
    {
        add[2 * v] += add[v];
        add[2 * v + 1] += add[v];
        f[v] = getf(v, tl, tr);
        s[v] = gets(v, tl, tr);
        add[v] = 0;
    }

    void update(int v, int tl, int tr, int l, int r, int d)
    {
        if (tl == l && tr == r)
        {
            add[v] += d;
            return;
        }
        push(v, tl, tr);
        int tm = (tl + tr) / 2;
        if (r <= tm) update(2*v, tl, tm, l, r, d);
        else if (l > tm) update(2*v+1, tm+1, tr, l, r, d);
        else
        {
            update(2*v, tl, tm, l, tm, d);
            update(2*v+1, tm+1, tr, tm+1, r, d);
        }
        s[v] = gets(2*v, tl, tm) + gets(2*v+1, tm+1,tr);
        f[v] = getf(2*v, tl, tm) + getf(2*v+1, tm+1, tr);
    }

    LD F()
    {
        return getf(1, 0, N - 1);
    }

} tree;

vector<int> X[N/2];
int n, a, b;

inline void addPt(int y)
{
    tree.update(1, 0, N - 1, y, y + b - 1, +1);
}

inline void erase(int y)
{
    tree.update(1, 0, N - 1, y, y + b - 1, -1);
}

int main()
{
    //freopen("input.txt","r",stdin);
    //freopen("output.txt","w",stdout);


    scanf("%d%d%d", &n, &a, &b);
    for(int i = 0; i < n; ++i)
    {
        int x, y;
        scanf("%d%d", &x, &y);
        X[x].pb(y);
    }
    /*
    n = 200000;
    a = 1000000;
    b = 1000000;
    for(int i = 0; i < n; ++i)
    {
        int x = (rand() * rand() + rand()) % a;
        int y = (rand() * rand() + rand()) % a;
        X[x].pb(y);
    }
    */
    for(int i = 0; i < sz(X[0]); ++i) addPt(X[0][i]);
    LD ans = 0.0;
    for(int pos = 1; pos < N; ++pos)
    {
        ans += tree.F();
        if (pos < N / 2) for(int i = 0; i < sz(X[pos]); ++i) addPt(X[pos][i]);
        if (pos >= a && pos - a < N / 2) for(int i = 0; i < sz(X[pos - a]); ++i) erase(X[pos-a][i]);
    }
    cout << fixed << setprecision(9) << ans / (LD)n / (n - 1) * 2.0 << endl;

    return 0;
}