#include <iostream>
using namespace std;
long long int ggg;
long long int n, x;
long long int pages(long long int nd, long long int first)
{
long long int tenpow = 1;
long long int ndig = 0;
long long int t = first;
while(t > 0)
{
t = t/10; // 10
tenpow *= 10;
ndig += 1;
}
long long int sum = 0;
long long int last = first - 1 + nd / ndig; // ndig
while(last >= tenpow)
{
sum += tenpow - first;
nd -= (tenpow - first) * ndig;
first = tenpow;
tenpow *= 10;
ndig += 1;
last = first - 1 + nd / ndig; // ndig
}
if(nd % ndig > 0)
{
return -1;
}
return sum + (last - first + 1);
}
int main()
{
cin >> ggg;
for(long long int i=0;i<ggg;i++)
{
cin >> n >> x;
cout << pages(n, x) << endl; // n - nd, x - first
}
return 0;
}
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