Power x Time

#include <algorithm>
#include <iostream>
#include <math.h>
#include <stdio.h>
#include <string.h>
#include <string>
#include <vector>
#define ll long long int
#define INF 999999999

using namespace std;

struct Program{
    ll power, time;

    Program(ll _power, ll _time){
        power = _power;
        time = _time;
    }
};

ll f, p, e, a, tmpE, tmpJ;

int main(void) {
    freopen("in.in", "r", stdin);
    ios::sync_with_stdio(0);
    while((cin >> f >> p >> e >> a) && (f + p + e + a)){
        vector<Program> programs[p + 1];
        for(int i = 0; i < p; i++){
            for(int j = 0; j < f; j++){
                cin >> tmpE >> tmpJ;
                programs[i].push_back(Program(tmpE, tmpJ));
            }
        }
        ll ans = 0;
        int actual_freq = 1;
        for(int i = 0; i < p; i++){
            int miN = INF;
            int idx = actual_freq;
            for(int j = 0; j < f; j++){
                ll prod = programs[i][j].power * programs[i][j].time;
                if(prod < miN){
                    if(j + 1 != actual_freq){
                        if(prod + (e * a) < miN){
                            miN = prod + (e * a);
                            idx = j + 1;
                        }
                    }else{
                        miN = prod;
                        idx = j + 1;
                    }
                }
            }
            actual_freq = idx;
            ans += miN;
        }
        cout << ans << "\n";
    }
    return 0;
}