#include <bits/stdc++.h>
#include <experimental/random>
#include <random>
//#include <ext/pb_ds/assoc_container.hpp>
//using namespace __gnu_pbds;
using namespace std;
using ld = long double;
using ll = long long;
const ll INF = 2e9, MOD = 1e9 + 7;
void solve();
signed main() {
#ifdef LOCAL
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
ios::sync_with_stdio(false);
cin.tie(0);
int q = 1;
//cin >> q;
while (q--) {
solve();
}
}
void solve() {
ll n, k;
cin >> n >> k;
vector<pair<ll, ll>> c;
ld ans = 0;
for (int i = 0; i < n; i++) {
ll a, b; cin >> a >> b;
ans += a;
if (b == -1) b = INF;
c.emplace_back(b, -a);
}
sort(c.begin(), c.end());
vector<ll> sm(n + 1);
for (ll i = n - 1; i >= 0; i--) {
sm[i] = sm[i + 1] - c[i].second;
}
ld time = 0;
for (int i = 0; i < n; i++) {
time += (ld)c[i].first / (ld)(i + 1);
ans = min(ans, time + (ld)sm[i + 1] / (ld)(i + 2));
}
cout << fixed << setprecision(9) << ans;
}
