#include <iostream>
using namespace std;
int main() {
int e, f, c;
cin >> e >> f >> c;
cout << (int)((e + f)/(c - 1 + 0.0001));
return 0;
}
I2luY2x1ZGUgPGlvc3RyZWFtPgp1c2luZyBuYW1lc3BhY2Ugc3RkOwoKaW50IG1haW4oKSB7IAoJaW50IGUsIGYsIGM7CgljaW4gPj4gZSA+PiBmID4+IGM7Cgljb3V0IDw8IChpbnQpKChlICsgZikvKGMgLSAxICsgMC4wMDAxKSk7CglyZXR1cm4gMDsKfQ==