#include<bits/stdc++.h>
using namespace std;
// define
#define execute cerr << " Time: " << fixed << setprecision(6) << (1.0 * clock() / CLOCKS_PER_SEC) << "s\n";
#define ll long long
#define ld double
#define ii pair<int,int>
#define se second
#define fi first
#define iii pair<int,ii>
#define all(v) v.begin(),v.end()
#define bit(x,i) (((x)>>(i))&1LL)
#define flip(x,i) ((x)^(1LL<<(i)))
#define ms(d,x) memset(d,x,sizeof(d))
#define sitingfake 1
#define orz 1
#define visit visited
#define left __left
#define right __right
//constant
const ll mod = 1e9 + 7;
const long long linf = 4557430888798830399;
const int inf = 1061109567;
const int maxarr = 1e6 + 5;
int dx[] = {0 , -1 , 0 , 1};
int dy[] = {-1 , 0 , 1 , 0};
template<typename T> bool maximize(T &a, const T &b)
{
if(a < b) {a = b; return 1;}
return 0;
}
template<typename T> bool minimize(T &a, const T &b)
{
if(a > b) {a = b; return 1;}
return 0;
}
inline void Plus(ll & a ,ll b)
{
b %= mod;
a += b;
if(a >= mod) a -= mod;
if(a < 0) a += mod;
return;
}
inline void Mul(ll & a, ll b)
{
a %= mod; b %= mod;
a *= b;
a %= mod;
return;
}
//code
const int maxn = 5e4 + 7;
vector <ii> a[maxn] , arev[maxn];
int n , m , q , k;
int ans[maxn] , mask[maxn];
int id[20][maxn] , timer[20];
vector <ii> pos[20];
vector <int> dist1 , dist2;
struct query
{
int l , r;
int id;
};
vector <vector<query>> Q[20];
void Init(int l , int r , int lv)
{
if(l > r) return;
if(l == r) return;
int mid = (r + l) >> 1;
pos[lv].push_back(ii(mid , timer[lv]));
id[lv][mid] = timer[lv];
timer[lv]++;
for(int i = mid + 1; i <= r; i++)
{
mask[i] |= (1 << lv);
}
Init(l , mid , lv + 1);
Init(mid + 1, r , lv + 1);
}
void dij(int l , int r ,vector <int> &dist , int s , bool f)
{
for(int i = l ; i <= r; i++) dist[i] = inf;
dist[s] = 0;
priority_queue <ii , vector <ii> , greater<ii>> q;
q.push(ii(0 , s));
while(!q.empty())
{
int u = q.top().se;
int cost = q.top().fi;
q.pop();
if(cost > dist[u]) continue;
if(f)
{
for(ii i : a[u])
{
int v = i.fi;
int w = i.se;
if(v < l || v > r) continue;
if(minimize(dist[v] , dist[u] + w))
{
q.push(ii(dist[v] , v));
}
}
}
else
{
for(ii i : arev[u])
{
int v = i.fi;
int w = i.se;
if(v < l || v > r) continue;
if(minimize(dist[v] , dist[u] + w))
{
q.push(ii(dist[v] , v));
}
}
}
}
}
void DnC(int l , int r , int lv)
{
if(l > r) return;
if(l == r)
{
return;
}
int mid = (r + l) >> 1;
int pos = mid;
while(pos <= r && abs((pos / k) - (mid / k)) <= 2)
{
dij(l , pos , dist1 , pos , 0);
dij(pos , r , dist2 , pos , 1);
for(query i : Q[lv][id[lv][mid]])
{
if(i.l <= pos && pos <= i.r)
{
minimize(ans[i.id] , dist1[i.l] + dist2[i.r]);
}
}
pos++;
}
DnC(l , mid , lv + 1);
DnC(mid + 1, r , lv + 1);
}
void solve(void)
{
cin >> k >> n >> m >> q;
for(int i = 1; i <= m; i++)
{
int u , v , w;
cin >> u >> v >> w;
u++;
v++;
a[u].push_back(ii(v , w));
arev[v].push_back(ii(u , w));
}
Init(1 , n , 0);
for(int i = 0; i <= 19; i++)
{
Q[i].resize(timer[i] + 2);
sort(all(pos[i]));
// cout << i << endl;
//
// for(ii i : pos[i])
// {
// cout << i.fi << " " << i.se << endl;
// }
//
// cout << endl;
}
for(int i = 1; i <= q; i++)
{
int u , v;
cin >> u >> v;
u++;
v++;
if(u < v)
{
int b = __builtin_ctz(mask[u] ^ mask[v]);
ii tmp = *(lower_bound(all(pos[b]) , ii(u , 0)));
if(tmp.fi < v)
{
Q[b][tmp.se].push_back({u , v , i});
}
}
else if(u == v)
{
ans[i] = 0;
}
}
dist1 = dist2 = vector <int> (n + 2 , inf);
ms(ans , 0x3f);
DnC(1 , n , 0);
for(int i = 1; i <= q; i++)
{
if(ans[i] == inf)
{
cout << "-1\n";
}
else cout << ans[i] << "\n";
}
}
/**
**/
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
#define task ""
if(fopen(task".inp","r"))
{
freopen(task".inp","r",stdin);
freopen(task".out","w",stdout);
}
int tc; tc = 1;
while(tc--) solve();
//execute;
}
