#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define pb emplace_back
#define AI(i) begin(i), end(i)
template<class T> bool chmin(T &a, T b) { return b < a && (a = b, true); }
template<class T> bool chmax(T &a, T b) { return a < b && (a = b, true); }
#ifdef KEV
#define DE(args...) kout("[ " + string(#args) + " ] = ", args)
void kout() { cerr << endl; }
template<class T, class ...U> void kout(T a, U ...b) { cerr << a << ' ', kout(b...); }
template<class T> void debug(T l, T r) { while (l != r) cerr << *l << " \n"[next(l)==r], ++l; }
#else
#define DE(...) 0
#define debug(...) 0
#endif
const int MAX_N = 600010;
#include "sorting.h"
int n, a[MAX_N], *s, *p, *q;
int *sx, *sy;
vector<pair<int,int>> count_cost(int *s) {
vector<int> a(s, s+n);
vector<pair<int,int>> ret;
for (int i = 0;i < n;++i) {
while (a[i] != i) {
int x = i, y = a[i];
swap(a[x], a[y]);
ret.pb(a[x], a[y]);
}
}
return ret;
}
int vx[MAX_N], vy[MAX_N], pos[MAX_N], pv[MAX_N], qv[MAX_N];
void mswap_pos(int x, int y) {
swap(a[x], a[y]);
swap(pos[ a[x] ], pos[ a[y] ]);
}
bool valid(int len) {
copy(s, s+n, a);
for (int i = 0;i < len;++i) {
swap(a[ sx[i] ], a[ sy[i] ]);
vx[i] = a[ sx[i] ], vy[i] = a[ sy[i] ];
}
auto swv = count_cost(a);
if (swv.size() > len) return false;
while (swv.size() < len) swv.pb(0, 0);
copy(s, s+n, a);
for (int i = 0;i < n;++i) pos[ a[i] ] = i;
for (int i = 0;i < len;++i) {
mswap_pos(sx[i], sy[i]);
auto [x, y] = swv[i];
mswap_pos( pos[x], pos[y] );
}
for (int i = 0;i < n;++i) assert(i == a[i]);
return true;
}
int findSwapPairs(int N, int S[], int M, int X[], int Y[], int P[], int Q[]) {
p = P, q = Q, s = S, sx = X, sy = Y;
n = N;
for (int i = 0;i < N;++i)
DE(sx[i], sy[i]);
int l = 0, r = n, mid;
while (l < r) {
mid = l + r >> 1;
if (valid(mid))
r = mid;
else
l = mid+1;
}
assert(valid(l));
valid(l);
DE(l);
return l;
}
