n, d, t = map(int, input().split())
p =[list(map(int, input().split())) for i in range(n)]
c = 0
i = 0
r = []
while c < t:
    r.append(c)
    c += d
    for j in p:
        if j[0] < c < j[1]:
            c = j[0]
            break

r.append(t)
print(len(r))