// Victor and Machine.cpp
#include <ios>
#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <cstdio>
#include <cwchar>
#include <iosfwd>
#include <limits>
#include <locale>
#include <memory>
#include <string>
#include <vector>
#include <cassert>
#include <ciso646>
#include <climits>
#include <clocale>
#include <complex>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdlib>
#include <cstring>
#include <cwctype>
#include <fstream>
#include <iomanip>
#include <istream>
#include <numeric>
#include <ostream>
#include <sstream>
#include <utility>
#include <iostream>
#include <iterator>
#include <valarray>
#include <algorithm>
#include <exception>
#include <stdexcept>
#include <streambuf>
#include <functional>
#define LL long long
#define lson l, m, rt<<1
#define rson m+1, r, rt<<1|1
#define PI 3.1415926535897932626
#define EXIT exit(0);
#define PAUSE system("pause");
#define DEBUG puts("Here is a BUG");
#define SYNC_CLOSE ios::sync_with_stdio(false);
#define what_is(x) cout << #x << " is " << x << endl;
#define CLEAR(name, init) memset(name, init, sizeof(name));
const double eps = 1e-8;
const int MAXN = (int)1e9 + 5;
using namespace std;
int main(int argc, char const *argv[]) {
#ifndef ONLINE_JUDGE
    freopen("D:\\Documents\\Disk_Synchronous\\Programs\\Acm\\input.txt", "r", stdin);
#endif
    int x, y, w, n;
    while(cin >> x >> y >> w >> n) {
        int t = 0, open = 0;
        while(n) {
            if (t - open == 0 || (t - open) % w == 0) {
                n--;
                if (n == 0) break;
            }
            if (t - open == x) {
                t += y;
                open = t;
                continue;
            }
            t++;
        }
        cout << t << endl;
    }
    return 0;
}