Use these functions for debugging
int f(int x,int y,int z)
{
    int i;
if (z==0) return 1;
for (i=x;i<=y;i++)
{
if (i>z) break;
if (f(x,y,z-i)==1) return 1;
}
return 0;
}
int ff(int x,int y,int l,int r)
{
int z=0;
for (int k=l;k<=r;k++) z+=f(x,y,k);
return z;
}
also:
to verivy k*x>a for big numbers is better to use:
k>=floor(a/x) if a%x!=0
k>a/x if a%x==0
because k*x can generate overflow

I got Ac after using all attention to boundary values 10^18.

Edited by author 11.10.2009 21:19