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Cod sursa(job #596640)
#include<stdio.h>
int sum,n,e[1000001];
int main() {
int i,j;
freopen("fractii.in","r",stdin);
freopen("fractii.out","w",stdout);
scanf("%d",&n);
for(i=2;i<=n;++i)
e[i]=i;
for(i=2;i<=n;++i)
if(e[i]==i)
for(j=i;j<=n;j+=i)
e[j]=e[j]/i*(i-1);
for(i=2;i<=n;++i)
sum+=e[i];
sum*=2;
printf("%d\n",sum+1);
return 0;
}