cf965c Greedy Arkady

#include <iostream>
using namespace std;
typedef long long ll;
ll n, k, m, d, ans;
int main(){
    cin>>n>>k>>m>>d;
    for(int i=1; i<=d; i++){
        ll x=n/(k*(i-1)+1);
        if(x==0)    break;
        x = min(x, m);
        ll tms=n/x;
        if(tms<(i-1)*k+1)   continue;
        ans = max(ans, i*x);
    }
    cout<<ans<<endl;
    return 0;
}