#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
int main()
{
	int a,b,c;
	cin>>a>>b>>c;
	int minv=a/c,maxv=b/c;
	if(a==b&&b==c)
	{
		cout<<a;
	}
	else if(maxv>minv)
	{
		cout<<(minv+1)*c;
	}
	else
	{
		cout<<-1;
	}
	return 0;	
}