#include "fstream"
using namespace std;
ifstream cin("input.txt");
ofstream cout("output.txt");

int main()
{long long n,m,a,b,s,i,j;
int z[10001][10001];
cin>>n>>m>>a>>b;
for (i=1;i<=n;i++)
for (j=1;j<=m;j++) z[i][j]=0;

while (! cin.eof())
{cin>>i>>j;
z[i][j]=1;
}

s=0;
for (i=1;i<=n;i++)
{
for (j=1;j<=m;j++)
s=s+a*z[i][j];
a=a-b;
}
s=100;
cout<<s<<endl;
return 0;
}