milkpailssilver

#pragma GCC optimize ("O3")
#pragma GCC target("sse4")
#include <bits/stdc++.h>
#define f first
#define s second
#define pb push_back
#define mp make_pair
#define ts to_string
#define ub upper_bound
#define lb lower_bound
const char nl = '\n';
using namespace std;
using ll = long long;
using vi = vector<int>;
using vl = vector<ll>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using str = string;
//The following debugging code was taken from Benjamin Qi's template :)
str ts(char c) { return str(1,c); }
str ts(bool b) { return b ? "true" : "false"; }
str ts(const char* s) { return (str)s; }
str ts(str s) { return s; }
template<class A> str ts(complex<A> c) {
    stringstream ss; ss << c; return ss.str(); }
str ts(vector<bool> v) {
    str res = "{"; for(int i = 0;i < (int)v.size(); i++) res += char('0'+v[i]);
    res += "}"; return res; }
template<size_t SZ> str ts(bitset<SZ> b) {
    str res = ""; for(int i = 0; i < b.size(); i++) res += char('0'+b[i]);
    return res; }
template<class A, class B> str ts(pair<A,B> p);
template<class T> str ts(T v) {
    bool fst = 1; str res = "{";
    for (const auto& x: v) {
        if (!fst) res += ", ";
        fst = 0; res += ts(x);
    }
    res += "}"; return res;
}
template<class A, class B> str ts(pair<A,B> p) {
    return "("+ts(p.f)+", "+ts(p.s)+")"; }
void DBG() { cerr << "]" << endl; }
template<class H, class... T> void DBG(H h, T... t) {
    cerr << ts(h); if (sizeof...(t)) cerr << ", ";
    DBG(t...); }

#ifdef LOCAL
#define dbg(...) cerr << "LINE(" << __LINE__ << ") -> [" << #__VA_ARGS__ << "]: [", DBG(__VA_ARGS__)
#else
#define dbg(...) 0
#endif
//CODE STARTS HERE-----------------------------------------------------------------------------------------//
int x,y,k,m,d[205][205];
queue<array<int,3>> q;
bool check(int a, int b){
    if(d[a][b] != -1)
        return false;
    return 1;
}
signed main(){
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    freopen("pails.in", "r", stdin);
    freopen("pails.out", "w", stdout);
    memset(d, -1, sizeof(d));
    cin >> x >> y >> k >> m;
    q.push({0,0,0});
    while(!q.empty()){
        array<int, 3> cur = q.front();
        if(cur[2] > k) break;
        q.pop();
        d[cur[0]][cur[1]] = cur[2];
        if(check(cur[0], 0)){
            q.push({cur[0], 0, cur[2] + 1});
        }
        if(check(0, cur[1])){
            q.push({0, cur[1], cur[2] + 1});
        }
        if(check(cur[0], y)){
            q.push({cur[0], y, cur[2] + 1});
        }
        if(check(x, cur[1])){
            q.push({x, cur[1], cur[2] + 1});
        }
        int nextx = cur[0] + cur[1];
        int nexty = (cur[0] + cur[1])-x;
        nextx = (nextx>x)?x:nextx;
        nexty = (nexty >= 0)?nexty:0;
        if(check(nextx, nexty)){
            q.push({nextx, nexty, cur[2] + 1 });
        }
        nextx = (cur[0] + cur[1])-y;
        nexty = (cur[0] + cur[1]);
        nexty = (nexty>y)?y:nexty;
        nextx = (nextx >= 0)?nextx:0;
        if(check(nextx, nexty)){
            q.push({nextx, nexty, cur[2] + 1 });
        }
    }
    int ans = 1e9;
    for(int i =0; i<=100; i++){
        for(int j = 0; j <=100; j++){
            if(d[i][j] != -1 && d[i][j] <= k){
                ans = min(ans, abs(m-i-j));
            }
        }
    }
    cout << ans << nl;
}