Example

Input

100 1 0
50 100


Output

14.57738
d, n, b = map(int, input().split())
O = [list(map(int, input().split())) for i in range(n)]

def solve(b):
    l = d / (b + 1)
    idx = 0
    vx2 = 10**9
    for i in range(b + 1):
        while idx < n and O[idx][0]*(b+1) <= d*(i+1):
            p, h = O[idx]
            p -= l*i
            vx2 = min(vx2, p*(l - p) / (2 * h))
            idx += 1
    if vx2 == 0:
        return 10**9
    if l <= vx2 * 2:
        return l
    return vx2 + l**2 / (4*vx2)
ans = 10**9
for i in range(0, b+1):
    ans = min(ans, solve(i))
import math
print(math.sqrt(ans))