Added older advents

advent_of_code_2019/day1/main1.cc

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+#include <iostream>
+
+using namespace std;
+
+int required_fuel(int mass)
+{
+    return (mass / 3) - 2;
+}
+
+int main(int argv, char **argc)
+{
+    int sum = 0;
+
+    while (!cin.eof())
+    {
+        int mass;
+        cin >> mass;
+
+        cout << mass << " requires " << required_fuel(mass) << "\n";
+
+        sum += required_fuel(mass);
+    }
+
+    cout << "Total required fuel: " << sum << "\n";
+}