n, s = map(int, input().split())
dem = max(0, n - (s + 162) + 1)
for x in range(s, min(n, s+161) + 1):
if x - sum([int(u) for u in str(x)]) >= s:
dem += 1
print(dem)
#include <bits/stdc++.h>
using namespace std;
#define ll long long
int sumOfDig(ll num)
{
int sum = 0;
while (num)
{
sum += num % 10;
num /= 10;
}
return sum;
}
ll diff(ll num)
{
return num - sumOfDig(num);
}
bool isValid(ll num, ll s)
{
return s <= diff(num);
}
int main()
{
ll n, s;
cin >> n >> s;
ll l, r, m;
l = 0;
r = n;
ll ans = -1;
while (l <= r)
{
m = l + (r - l) / 2;
if (isValid(m, s))
{
r = m - 1;
ans = m;
}
else
{
l = m + 1;
}
}
printf("%lld", n < n - ans + 1 ? 0 : n - ans + 1);
return 0;
}
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