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#include <bits/stdc++.h>
#define endl "\n"
#define ll long long
#define IO ios::sync_with_stdio(0); cin.tie(0); cout.tie(0)
using namespace std;




int main() {
    IO;
    ll a,b,c,d; // changing the data type here from int to ll changed the verdict from wrong on test case 4 to accepted. How??
    cin>>a>>b>>c>>d;
    ll result = (a*b)-(c*d);
    cout<<"Difference = "<<result;
    }