MAXPRO (HSGHN L9 2020-2021)

#include <iostream>
#include <cstdio>

using namespace std;

using ll = long long;
using ld = long double;
ll a, b, c, m;

void Read()
{
    cin >> a >> b >> c >> m;
}

/// a <= b <= c
void Sort()
{
    if (a > b)
        swap(a, b);
    if (b > c)
        swap(b, c);
    if (a > b)
        swap(a, b);
}

ll Mul(ll a, ll b, ll mod)
{
    ll q = (ld)a * b / mod;
    ll r = a * b - q * mod;
    return (r + mod) % mod;
}

void Solve()
{
    if (b > 0)
        cout << Mul(b, c, m);
    else if (b < 0)
        cout << Mul(a, b, m);
    else
        cout << 0;
}

int32_t main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    freopen("MAXPRO.INP", "r", stdin);
    freopen("MAXPRO.OUT", "w", stdout);

    Read();
    Sort();
    Solve();
}