#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC target("avx2")
#define forn for(int i=1;i<=n;i++)
#define Yes cout<<"YES\n"
#define No cout<<"NO\n"
#define YES cout<<"YES\n"
#define NO cout<<"NO\n"
#define pb push_back
#define sp setprecision
#define int long long
#define ll long long
#define nn '\n'
using namespace std;
const int N=1e6+10;
int a[N];
const int MOD=1e9+7;
string ab="abcdefghijklmnopqrstuvwxyz";
int binpow(int n, int k) {
int ans = 1;
while (k > 0) {
if (k % 2 == 1) {
ans = (ans * n) % MOD;
}
n = (n * n) % MOD;
k /= 2;
}
return ans;
}
int sumofnum(int x) {
int sum=0;
while (x>1) {
sum+=x%10;
x/=10;
}
return sum;
}
//vector <int> g[N];
void al(){
int n;
cin>>n;
int cnt=0;
int x=0;
int mn=n;
int mnx=1e9;
int mxn=0;
for(int i=1;i<=n;i++){
cin>>a[i];
}
for(int i=1;i<=n;i++){
if(a[i]>a[i+1]) cnt++;
}
bool ok=1;
for(int i=1;i<=n;i++){
if(a[i]!=i) ok=0;
}
mn=min(mn,cnt);
if(ok) cout<<0;
else cout<<mn;
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int t=1;
// cin>>t;
while(t--) {
al();
}
}
/*
2
2 2 3 3 1 1
*/
