#include <iostream>
 #include <iomanip>
 #include <cmath>
 #include <algorithm>
 #include <cstdlib>
 #include <limits.h>
 #include <string>

 #define ll long long

 using namespace std;
 void Fast_IO();
 void Rofyda_Elghadban(){
   #ifndef ONLINE_JUDGE
        freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
    #endif
}



int main()
 {   Rofyda_Elghadban();
 //Fast_IO();
 //freopen("input.txt","r",stdin);
 //freopen("output.txt","r",stdout);
 ll a,b,x,sum=0;
 cin>>a>>b>>x;
 if(b>=a){
  if(b==x){
    cout<<b;
  }else{
    for(ll i=a;i<=b;i++){
      if(i%x==0){
        sum+=i;
      }
    }cout<<sum;
  }
 }else if(b<a){
  for(int i=b;i<=a;i++){
    if(i%x==0){
      sum+=i;
    }
  }cout<<sum;
 }



 return 0;
 }