753 B | 753 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():
h, k, v, s = mii()
dis = 0
while h > 0:
v += s
v -= max(1, int(v // 10))
if v >= k:
h += 1
elif 0 < v < k:
h -= 1
if h == 0:
v = 0
else:
h = v = 0
dis += v
if s > 0:
s -= 1
p(dis)
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
ret = solve()