import java.util.*;
import java.lang.*;
import java.io.*;
class Main
{
{
int e, f, c;
Scanner in
= new Scanner
(System.
in); e = in.nextInt();
f = in.nextInt();
c = in.nextInt();
System.
out.
print((int)((e
+ f
)/(c
- 1 + 0.0001)));
}
}
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