636 B | 636 chars
import sys
from math import sqrt, pi, sin, factorial, ceil, floor
from datetime import datetime, timedelta
# sys.setrecursionlimit(10**7)
BLANK = " "
# inp = input
inp = lambda : sys.stdin.readline().rstrip()
mii = lambda x = BLANK : [*map(int,inp().split(x))]
mfi = lambda x = BLANK : [*map(float,inp().split(x))]
ii = lambda : int(inp())
fi = lambda : float(inp())
p = print
def solve():
n, x = mii()
l = [mii() for _ in range(n + 1)]
ret = 0
for a, i in l:
ret *= x
ret += a
ret %= 1000000007
p(ret)
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
ret = solve()