Cod sursa(job #284684)
Utilizator | Puscas Sergiu harababurel | Data | 21 martie 2009 21:31:52 |
---|---|---|---|
Problema | Fractii | Scor | 100 |
Compilator | cpp | Status | done |
Runda | Arhiva de probleme | Marime | 0.59 kb |
#include<stdio.h>
long n;
long e[1000010];
void ciur()
{
long i,j;
for(i=2;i<=n;i++)
e[i]=i;
for(i=2;i<=n;i++)
if(e[i]==i)//i este prim
{
for(j=i;j<=n;j+=i)
e[j]=e[j]/i*(i-1);
}
}
int main()
{
freopen("fractii.in","r",stdin);
freopen("fractii.out","w",stdout);
scanf("%ld",&n);
ciur();
long i;
long long s=0;
for(i=2;i<=n;i++)
s=s+2*e[i];
printf("%lld\n",s+1);
return 0;
}