Problem_#70_Totient_permutation.cpp

#include <cstdio>
#include <iostream>
#include <sstream>
#include <string>
#include <cmath>
#include <cassert>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <deque>
using namespace std;
typedef long long ll;
typedef pair<double, double> dd;
typedef pair<int, int> ii;
typedef pair<int, ii> iii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<vi> vvi;
typedef vector<vii> vvii;

int isPerm(int a, int b){
	vi as(10, 0);
	while(a != 0){
		as[a%10]++;
		a /= 10;
	}
	while(b != 0){
		as[b%10]--;
		b /= 10;
	}
	for(int i=0;i<10;i++){
		if(as[i] != 0) return false;
	}
	return true;
}

int main(){
	int n; cin >> n;
	vi ps(n, 0);
	vi eus(n);
	for(int i=0;i<n;i++) eus[i] = i;

	for(int i=2;i<n;i++){
		if(!ps[i]){
			for(int j=i;j<n;j+=i){
				ps[j] = 1;
				eus[j] -= eus[j]/i;
			}
		}
	}

	vi v(n);
	int best = -1;
	for(int i=2;i<n;i++){
		v[i] = eus[i];
		if(best == -1 || double(i)/v[i] < double(best)/v[best]){
			if(isPerm(v[i], i)){
				best = i;
			}
		}
	}
	cout << best <<endl;
}