Cod sursa(job #144381)
Utilizator | hulparu adrian hulparuadrian | Data | 27 februarie 2008 15:41:04 |
---|---|---|---|
Problema | Fractii | Scor | 0 |
Compilator | cpp | Status | done |
Runda | Arhiva de probleme | Marime | 0.49 kb |
#include<iostream>
#include<fstream>
using namespace std;
ifstream f("fractii.in");
ofstream g("fractii.out");
int ciur[1000001],n;
long sol;
void ciur_erath(int n)
{
for(int i=2;i*i<=n;i++)
{if (!ciur[i])
for(int l=2;l*i<=n;l++)
{ciur[l*i]=1;sol--;}}
}
int main()
{
f>>n;
long sol=(n-1)*n/2;
sol++;
ciur_erath(n);
g<<sol;
f.close();
g.close();
return 0;
}