func_code_string: #include <bits/stdc++.h>   using namespace std;   int ar[100001];   int main() {     ios::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     long long t, n, m;     cin >> t;     while (t--) {       cin >> n >> m;       long long val = n / m;       int a = m % 10, cnt = 0;       ar[cnt++] = a;       int b = 2;       while ((a * b) % 10 != a) {         ar[cnt++] = (a * b) % 10;         b++;       }       long long sum = 0;       for (int i = 0; i < cnt; i++) sum += ar[i];       long long ans = 0;       ans += sum * (val / cnt);       for (int i = 0; i < (val % cnt); i++) ans += ar[i];       cout << ans << endl;     }   }   