Competitve-Programming/C_Book_Reading.cpp at main · arshchouhan/Competitve-Programming · GitHub

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#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;


#include <iostream>
#include <vector>
using namespace std;

int main()
{
    int t;
    cin >> t;

    while (t--)
    {
        long long n, m;
        cin >> n >> m;

        long long k = n / m;

        vector<int> cycle;

        for (int i = 1; i <= 10; i++)
        {
            cycle.push_back((i * m) % 10);
        }

        long long cycleSum = 0;
        for (int x : cycle)
            cycleSum += x;

        long long fullCycle = k / 10;
        long long rem = k % 10;

        long long ans = fullCycle * cycleSum;

        for (int i = 0; i < rem; i++)
        {
            ans += cycle[i];
        }

        cout << ans << endl;
    }
}