khuyến mãi

include <bits/stdc++.h>

using namespace std; int main() { long long a, b = 0, c = 0; cin >> a; while (a > 0) { b += a; c += a; a = c/10*3; c %= 10; } cout << b; } tổng lẽ

include <bits/stdc++.h>

using namespace std;

int main() { long long n,s=0,i; cin>>n; for(i=1;i<=n;i++) { if(i%2==1) s+=i; } cout<<s; return 0; } tổng bội 13

include <bits/stdc++.h>

using namespace std;

int main() { long long l,r,s; cin>>l>>r; s=(l+r)(r-l+1)/2; while(l%13!=0) l++; while(r%13!=0) r--; long long n=(l+r)((r-l)/13+1)/2; cout<<s-n; }