#include<iostream>
#include<algorithm>
#include<vector>
#include<set>
#include<cmath>
#include<math.h>
#include<iomanip>
using namespace std;
#define int long long
typedef long double ld;
ld poww(ld a, int b) {
    if (b == 0) {
        return 1;
    }
    if (b % 2 == 0) {
        ld p = poww(a, b / 2);
        return p*p;
    }
    else {
        return a * poww(a, b - 1);
    }
}
signed main()
{
    cout << fixed << setprecision(10);
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    int n, m, t;
    cin >> n >> m >> t;
    ld r = 0;
    vector<pair<ld, ld > > a(n);
    for (int i = 0; i < n; ++i) {
        ld s, p;
        cin >> s >> p;
        r += s;
        a[i] = make_pair(p, s);
    }
    sort(a.begin() , a.end());
    int cnt = 0;
    ld l = 0;
    vector<ld> c(n);
    while (cnt < 1000) {
        ld mid = (r + l) / 2;
        int j = 0;
        ld mid1 = mid;
        while (mid1 > 0) {
            mid1 -= a[j].second;
            c[j] = a[j].second*(1000000.0 + a[j].first)/1000000.0;
            j++;
        }
        if (mid1 < 0) {
            c[j - 1] = (a[j-1].second+mid1)*(1000000.0+a[j-1].first)/1000000.0;
            j--;
        }
        int k = 0;
        bool check = true;
        ld t1 = t;
        while (k < m) {
            if (t1 < c[j]) {
                c[j] -= t1;
                c[j] *= (a[j].first+1000000.0)/1000000.0;
                k++;
                t1 = t;
                continue;
            }
            t1 -= c[j];
            c[j] = 0;
            j--;
            if (c[0] <= 0) {
                break;
            }
            c[j] *= poww((a[j].first + 1000000.0) / 1000000.0, k);
        }
        if (c[0] <= 0) {
            l = mid;
        }
        else {
            r = mid;
        }
        cnt++;
        c.clear();
        c.resize(n);
    }
    cout << l;
    return 0;
}