这个东西太好用了，感觉很多题都可以用这个东西来写暴力或乱搞.
#include <set>
#include <cmath>
#include <ctime>
#include <cstdio>
#include <algorithm>
#define ll long long
#define ull unsigned long long
#define setIO(s) freopen(s".in", "r" , stdin)
using namespace std;
set<ll>S;
set<ll>::iterator it;
int array[20]={2,3,5,7,11,13,17,19};
ll mult(ll x,ll y,ll mod)
{
ll tmp=(long double)x/mod*y;
return ((ull)x*y-(ull)tmp*mod+mod)%mod;
}
ll F(ll a,ll c,ll mod)
{
return (mult(a,a,mod)+c)%mod;
}
ll qpow(ll base,ll k,ll mod)
{
ll tmp=1;
for(;k;k>>=1,base=mult(base,base,mod)) if(k&1) tmp=mult(tmp,base,mod);
return tmp;
}
int isprime(ll x)
{
if(x<=1) return 1;
int k,i,j;
ll cur=x-1,a,pre;
for(k=0;cur%2==0;cur>>=1) ++k;
for(i=0;i<8;++i)
{
if(array[i]==x) return 1;
a=pre=qpow(array[i],cur,x);
for(j=1;j<=k;++j)
{
a=mult(pre,pre,x);
if(a==1&&pre!=1&&pre!=x-1) return 0;
pre=a;
}
if(a!=1) return 0;
}
return 1;
}
ll pollard_rho(ll x)
{
int k,step;
ll s=0,t=0,c=rand()%(x-1)+1,val=1,d;
for(k=1;;k<<=1,s=t,val=1)
{
for(step=1;step<=k;++step)
{
t=F(t,c,x);
val=mult(val,abs(t-s),x);
if(step%127==0)
{
d=__gcd(val,x);
if(d>1) return d;
}
}
d=__gcd(val,x);
if(d>1) return d;
}
}
void solve(ll x)
{
if(x<2) return;
if(isprime(x))
{
S.insert(x);
return;
}
ll p=x;
for(;p>=x;) p=pollard_rho(x);
for(;x%p==0;) x/=p;
solve(x),solve(p);
}
int main()
{
// setIO("input");
ll n,ans=1;
scanf("%lld",&n),solve(n);
for(it=S.begin();it!=S.end();it++)
{
ll cur=(*it);
for(;n%cur==0;) n/=cur,ans*=cur;
ans=ans/cur*(cur-1);
}
printf("%lld\n",ans);
return 0;
}
