Cod sursa(job #1131259)
Utilizator | Vlad Dimulescu vladvaldez | Data | 28 februarie 2014 18:55:51 |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 100 |
Compilator | cpp | Status | done |
Runda | Arhiva educationala | Marime | 0.48 kb |
#include <stdio.h>
using namespace std;
FILE *f=fopen("ciur.in","r");
FILE *g=fopen("ciur.out","w");
int n;
bool cr[1000005];
// p[i]==0 => 2*i+1 e prim
int ciur(int n)
{int i,nr=1,j;
/* for(i=2;i<=n;i+=1)
cr[i]=1;*/
for(i=1;((i*i)<<1)+(i<<1)<=n;i+=1)
if (cr[i]==0)
{
for(j=((i*i)<<1)+(i<<1);(j<<1)+1<=n;j+=(i<<1)+1)
cr[j]=1;
}
for (i=1;2*i+1<=n;i++)if (cr[i]==0) nr++;
return nr;
}
int main()
{
fscanf(f,"%d",&n);
fprintf(g,"%d",ciur(n));
return 0;
}