Sorting Railway Car

#include <bits/stdc++.h>

using namespace std;

int n;
vector<int> num;
unordered_map<int, int> mp;
int l;

int main(){
    //freopen("railwaycars.in", "r", stdin);

    cin >> n;
    num.resize(n+1);
    for(int i=0; i<n; i++){
        cin >> num[i];
        mp[num[i]] = mp[num[i]-1]+1;
        //cout << "num[i]: " << num[i] << ", mp[num[i]]: " << mp[num[i]] << '\n';
        l = max(l, mp[num[i]]);
    }
    cout << n-l << '\n';

    return 0;
}