Contest1343/D.cpp

#include<bits/stdc++.h>
 
using namespace std;
using LL=long long;
const int MAXN = 2e6 + 10;
vector<int> primes = {2, 3};
 
void init() {
    for (int k = primes.back() + 2; k <= MAXN; k += 2) {
        bool flag = true;
        for (auto p:primes) {
            if (p * p > k)break;
            if (k % p == 0) {
                flag = false;
                break;
            }
        }
        if (flag)primes.push_back(k);
    }
}
 
int main() {
    init();
    for (int n; cin >> n;) {
        map<int, int> k;
        for (auto p:primes) {
            if (p * p > n)break;
            while (n % p == 0) {
                ++k[p];
                n /= p;
            }
        }
        if (n > 1)k[n]++;
        LL ans = 1;
        for (auto p:k) {
            if (p.second == 1)ans *= (p.first - 1);
            else ans *= pow(p.first, p.second) - pow(p.first, p.second - 1);
 
        }
        cout << ans << endl;
    }
    return 0;
}