#include<bits/stdc++.h> using namespace std; #define int long long int n,s,ans; bool check(int k){ if(k>n||k==0)return 0; int t=k,sum=0; while(k){ sum+=k%10; k/=10; } return t-sum>=s; } signed main(){ cin>>n>>s; ans=0; int l=1,r=n; while(l<=r){ int mid=(l+r)>>1; if(check(mid)){ ans=mid; r=mid-1; } else l=mid+1; } if(ans==0)cout<<0<<endl; else cout<<n-ans+1<<endl; return 0; } /* 1：枚举每一位 2：二分 */