n, k, a = map(int, input().split())
l = [[*map(int, input().split())] for i in range(n)]
times = []
drinking_time = k // a
for t, s in l:
if drinking_time % t == 0:
d = drinking_time // t - 1
times.append(drinking_time + d * s)
else:
d = drinking_time // t
times.append(drinking_time + d * s)
print(min(times))