#include<bits/stdc++.h>
using namespace std;
int main(){
int n,m,a,q;
int b[10010];
cin>>n>>m>>a>>q;
for(int i=1;i<=q;i++)
{
cin>>b[i];
}
int mx=0;
for(int i=1;i<=q;i++)
{
int total_removed=(am)+(b[i]n)-(ab[i]);
int remaining=nm-total_removed;
mx=max(mx,remaining);
}
cout<<mx;
return 0;
}
