Created
January 7, 2017 02:41
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#include <bits/stdc++.h> | |
using namespace std; | |
typedef long long ll; | |
typedef vector<ll> vi; | |
ll N; | |
vi primes; | |
vector<bool> bs(10000000); | |
ll __sieve_size; | |
void sieve(ll upperbound) | |
{ | |
__sieve_size = upperbound+1; | |
fill(bs.begin(),bs.end(),false); | |
bs[0] = bs[1] = 1; | |
for(ll i = 2; i <= __sieve_size ; i++) | |
{ | |
if(!bs[i]) | |
{ | |
for(ll j = i * i ; j <= __sieve_size ; j+=i) | |
{ | |
bs[j] = 1; | |
} | |
primes.push_back(i); | |
} | |
} | |
} | |
bool isPrime(ll n) | |
{ | |
if(N <= __sieve_size) return bs[N]; | |
for(int i = 0; i < (int)primes.size();i++) | |
{ | |
if( N % primes[i] == 0) return false; | |
} | |
} | |
ll phi() | |
{ | |
ll result = N; // Initialize result as n | |
for (ll i= 0; primes[i]*primes[i] <= N; i++) | |
{ | |
if (N % primes[i] == 0) | |
{ | |
while (N % primes[i] == 0) | |
N /= primes[i]; | |
result -= result / primes[i]; | |
} | |
} | |
if (N > 1) | |
result -= result / N; | |
return result; | |
} | |
long long totient(long long n) { | |
if (n == 1) return 0; | |
long long ans = n; | |
for (int i = 0; primes[i] * primes[i] <= n; ++i) { | |
if ((n % primes[i]) == 0) { | |
while ((n % primes[i]) == 0) n /= primes[i]; | |
ans -= ans / primes[i]; | |
} | |
} | |
if (n > 1) { | |
ans -= ans / n; | |
} | |
return ans; | |
} | |
int main() | |
{ | |
sieve(55000); | |
while (cin >> N) | |
{ | |
cout << ( phi() >> 1 ) << endl; | |
} | |
} |
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