#include <cstdio>
#include <algorithm>
using namespace std;
int n, m, a, b, s;
int main() {
    freopen("bs.in", "r", stdin);
    freopen("bs.out", "w", stdout);
    while(scanf("%d %d %d %d", &n, &m, &a, &b) == 4) {
        if(n > m)
            swap(n, m), swap(a, b);
        //fprintf(stderr, "%d %d %d %d\n", n, m, a, b);
        if(a + b == 0)
            s = 0;
        else if(a == 0)
            s = min(m, b);
        else if(b == 0)
            s = min(n, a);
        else
            s = n + min(m, (n + 1) * b);
        printf("%d\n", s);
    }
    return 0;
}