#include<bits/stdc++.h> #define int long long using namespace std; int n,s,cnt=0; bool check(int x){ int sum=0,y=x; while(y!=0){ sum+=(y%10); y/=10; } if((x-sum)>=s) return true; else return false; } signed main(){ cin>>n>>s; int i=s; if(check(n)==0){ cout<<0<<endl; return 0; } for(;i<=n;i++){ if(check(i)) break; } cout<<n-i+1<<endl; return 0; }