#include <bits/stdc++.h>
using namespace std;
#include "sorting.h"
//macros
typedef long long ll;
typedef pair<int, int> ii;
typedef pair<ll, ll> lll;
typedef tuple<int, int, int> iii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<iii> viii;
typedef vector<ll> vll;
typedef vector<lll> vlll;
#define REP(a,b,c) for(int a=int(b); a<int(c); a++)
#define RE(a,c) REP(a,0,c)
#define RE1(a,c) REP(a,1,c+1)
#define REI(a,b,c) REP(a,b,c+1)
#define REV(a,b,c) for(int a=int(c-1); a>=int(b); a--)
#define INF 1e9
#define pb push_back
#define fi first
#define se second
#define sz size()
const int MX = 2e5+100;
int a[MX], sa[MX], ss[MX];
int b[MX];
int n;
int *S, *X, *Y;
void swapA(int x, int y) {
swap(a[x], a[y]);
sa[a[x]] = x;
sa[a[y]] = y;
}
void swapS(int x, int y) {
swap(S[x], S[y]);
ss[S[x]] = x;
ss[S[y]] = y;
}
int visited[MX];
void dfs(int u) {
if(visited[u]) return;
visited[u] = 1;
dfs(b[u]);
}
bool possibleSwaps(int swaps) {
RE(i,n) visited[i] = 0;
int cyc = 0;
RE(i,n) {
if(visited[i]) continue;
dfs(i);
cyc++;
}
if(n-cyc <= swaps) return 1;
return 0;
}
bool possible(int am) {
RE(i,n) a[i]=sa[i]=i;
RE(i,n) b[i] = S[i];
RE(i,am) {
swapA(sa[X[i]], sa[Y[i]]);
swap(b[X[i]], b[Y[i]]);
}
return possibleSwaps(am);
}
int findSwapPairs(int _n, int _S[], int m, int _X[], int _Y[], int P[], int Q[]) {
n=_n, S=_S, X=_X, Y=_Y;
int lb=0, ub=n;
while(lb != ub) {
int mid=(lb+ub)/2;
if(possible(mid)) ub=mid;
else lb=mid+1;
}
int times = lb;
possible(times);
RE(i,n) ss[S[i]] = i;
int R = 0; int curI = 0;
RE(i,times) {
R++;
swapA(X[i], Y[i]);
swapS(X[i], Y[i]);
int x=0, y=0;
while(x == y) {
if(curI == n) break;
x = ss[curI];
y = sa[curI];
curI++;
}
swapS(x, y);
P[R-1] = x;
Q[R-1] = y;
}
return R;
}
