luogu_2022 有趣的数

#include <cstdio>
#include <iostream>
using namespace std;
long long n,k,ans;
string m;

int main(){
    cin>>m>>k;
    long long x=0,sum=0,y=1;
    for(int i=0;i<m.size();i++){
        x=x*10+m[i]-48;
        sum+=x-y+1;
        y*=10;
    }
    if(k<sum){printf("0\n"); return 0;}
    if(k==sum){cout<<m<<endl; return 0;}
    long long i;
    for(i=1;i<=1000;i++){
        x*=10;
        sum+=x-y;
        if(sum>=k)break;
        y*=10;
    }
    if(i==1001){printf("0\n"); return 0;}
    sum-=x-y;
    x/=10;
    y+=k-sum;
    printf("%lld\n",y-1);
    return 0;
}