#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<ll,ll>;
#define rep(i, n) for(int i = 0; i < n; i++)
#define all(x) (x).begin(),(x).end()
template<class T>bool chmin(T&a, const T&b){if(a>b){a=b;return 1;}return 0;}
template<class T>bool chmax(T&a, const T&b){if(a<b){a=b;return 1;}return 0;}

int main(){
    ll a[3], m;
    cin >> a[0] >> a[1] >> m;
    ll ans = 0;
    a[2] = a[0] - a[1];
    rep(i,3){
        while(a[i]){
            a[i] /= m;
            if(i) ans -= a[i];
            else ans += a[i];
        }
        //cout << ans << endl;
    }
    cout << ans << endl;
    return 0;
}