#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <string>
#include <cmath>
#include <cstdio>
#include <iomanip>
#include <fstream>
#include <cassert>
#include <cstring>
#include <unordered_set>
#include <unordered_map>
#include <numeric>
#include <ctime>
#include <bitset>
#include <complex>
#include <random>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;

#ifdef DEBUG
    const int MAXN = 10;
    const int MAXLOG = 4;
    const int MAXSQRT = 4;
#else
    const int MAXN = 3e5;
    const int MAXLOG = 20;
    const int MAXSQRT = 400;
    #define cerr if (false) cerr
#endif

mt19937 rng(time(0));
#define double long double
const int INF = 1e9;
const int MOD = 1e9 + 7;

int n, a, b;
int x[MAXN];
double v[MAXN];
double can[MAXN];

inline void init() {

}

inline void solve() {
    init();
    for (int i = 0; i < n; i++) {
        cin >> x[i] >> v[i];
    }
    can[n - 1] = v[n - 1];
    for (int i = n - 2; i >= 0; i--) {
        double s = x[i + 1] - x[i];
        double t = (-can[i + 1] + sqrtl(can[i + 1] * can[i + 1] + 2 * b * s)) / b;
        can[i] = min(v[i], can[i + 1] + b * t);
    }
    double ans = 0;
    double cur = 0;
    for (int i = 0; i < n - 1; i++) {
        double f = can[i + 1];
        double s = x[i + 1] - x[i];
        {
            double t1 = (-cur + sqrtl(cur * cur + 2 * a * s)) / a;
            if (cur + t1 * a <= f) {
                cur += t1 * a;
                ans += t1;
                continue;
            }
        }
        double A = a * a + a * b;
        double B = 2 * cur * (a + b);
        double C = -f * f - 2 * b * s - cur * cur;
        double d1 = (-B + sqrtl(B * B - 4 * A * C)) / 2 * A;
        double d2 = (-B - sqrtl(B * B - 4 * A * C)) / 2 * A;
        double d;
        if (d2 < 0) {
            d = d1;
        }
        else {
            d = d2;
        }
        double t = (cur - f + a * d) / b;
        ans += t + d;
        cur = can[i + 1];
    }
    cout << ans << '\n';
}

signed main() {
    #ifdef DEBUG
        freopen("A.in", "r", stdin);
        freopen("A.out", "w", stdout);
    #else

    #endif
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    while (cin >> n >> a >> b)
        solve();
    return 0;
}