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  1. #include <iostream>
  2. using namespace std;
  3. int main(){
  4. long long n,a,b;
  5. cin>> n >> a >> b;
  6. unsigned long long d=(n-(n%a))/a, s1=(n/2)*(1+n), s2= a*0.5*d*(d+1), s3= d*b+0.5*d*(d-1);
  7. unsigned long long z= s1 -s2 +s3;
  8. cout << z;
  9. return 0;
  10. }
Success #stdin #stdout 0.01s 5296KB
stdin
Standard input is empty
stdout
15266643687350014464