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Cod sursa(job #533212)
#include<fstream>
using namespace std;
int n,i;
int a[1000001];
long long r;
ifstream f("fractii.in");
ofstream g("fractii.out");
void pi()
{
int j,i;
for(i=1;i<=n;++i){a[i]=i-1;}
for(i=2;i<=n;++i){for(j=2*i;j<=n;j+=i){a[j]-=a[i];}}
}
int main()
{
f>>n;
pi();
r = 1;
for(i=1;i<=n;i++){r+=2*a[i];}
g<<r;
f.close();g.close();
return 0;
}