import sys

# sys.setrecursionlimit(200005)
# sys.set_int_max_str_digits(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

# dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = -1-(-1 << 31)
# inf = -1-(-1 << 62)

# md = 10**9+7
md = 998244353

lim=10**18

n,p,k=LI()
dp=[-inf]*(k+1)
dp[0]=p
for _ in range(n):
    t,b=LI()
    for i in range(k)[::-1]:
        if t==1:
            dp[i+1]=max(dp[i+1],dp[i]+b)
        else:
            dp[i+1]=max(dp[i+1],dp[i]*2)
        if dp[-1]>lim:
            print(-1)
            exit()

print(dp[-1])