//by szh
#include<bits/stdc++.h>
#include <unordered_map>
using namespace std;
#define fi first
#define se second
#define pii pair<int,int>
#define pll pair<long long,long long>
#define pb push_back
#define debug(x) cerr<<#x<<"="<<x<<endl
#define pq priority_queue
#define inf 0x3f
#define rep(i,a,b) for (int i=a;i<(b);i++)
#define MP make_pair
#define SZ(x) (int(x.size()))
#define ll long long
#define mod 1000000007
#define ALL(x) x.begin(),x.end()
void inc(int &a,int b) {a=(a+b)%mod;}
void dec(int &a,int b) {a=(a-b+mod)%mod;}
int lowbit(int x) {return x&(-x);}
ll p0w(ll base,ll p) {ll ret=1;while(p>0){if (p%2ll==1ll) ret=ret*base%mod;base=base*base%mod;p/=2ll;}return ret;}
#include "sorting.h"
const int maxn = 6e5+10;
int n,m;
int a[maxn],b[maxn];
pii ans[maxn];
pii p[maxn];
deque <int> q[maxn];
int id[maxn];
pii pos[maxn];
vector <int> nxt;
pii qid[maxn];
bool check(int cnt) {
while (!nxt.empty())nxt.pop_back();
rep(i,0,n) {
while (!q[i].empty()) q[i].pop_back();
q[i].pb(i);
id[i] = i;
b[i] = a[i];
}
rep(i,0,cnt) {
int x=p[i].fi,y=p[i].se;
q[id[x]].pb(y);
q[id[y]].pb(x);
swap(id[x],id[y]);
qid[i] = {id[x],id[y]};
}
rep(i,0,n) {
pos[q[i].back()].fi = q[i].front();
pos[a[i]].se = i;
}
rep(i,0,n) if (pos[i].fi!=pos[i].se) nxt.pb(i);
rep(i,0,cnt) {
int x = p[i].fi,y=p[i].se;
swap(b[x],b[y]);
pos[b[x]].se = x,pos[b[y]].se = y;
q[qid[i].fi].pop_front(),q[qid[i].se].pop_front();
pos[q[qid[i].fi].back()].fi = q[qid[i].fi].front();
pos[q[qid[i].se].back()].fi = q[qid[i].se].front();
pii cur = {0,0};
while (!nxt.empty() and pos[nxt.back()].fi==pos[nxt.back()].se) nxt.pop_back();
if(!nxt.empty()) cur = pos[nxt.back()];
x = cur.fi,y=cur.se;
swap(b[x],b[y]);
pos[b[x]].se = x,pos[b[y]].se = y;
ans[i] = cur;
}
while (!nxt.empty() and pos[nxt.back()].fi==pos[nxt.back()].se) nxt.pop_back();
return nxt.empty();
}
int findSwapPairs(int N, int S[], int M, int X[], int Y[], int P[], int Q[]) {
n = N,m= M;
int l=0,r=M;
rep(i,0,n) a[i] =S[i];
rep(i,0,M) p[i] = {X[i],Y[i]};
while (l<r) {
int mid=l+r>>1;
if (check(mid)) r = mid;
else l = mid+1;
}
assert(check(l));
rep(i,0,l) P[i] = ans[i].fi, Q[i] = ans[i].se;
return l;
}
