Cod sursa(job #523594)
Utilizator | Data | 18 ianuarie 2011 17:04:26 | |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 30 |
Compilator | cpp | Status | done |
Runda | Arhiva educationala | Marime | 0.4 kb |
#include<stdio.h>
int n,prim[2000001],nr=0,i;
void primes(int n)
{
int i,j;
for(i=2;i<=n;++i) prim[i]=1;
for(i=4;i<=n;i+=2) prim[i]=0;
for(i=3; i*i<=n; i+=2)
if(prim[i])
for(j=i*i;j<=n;j+=i) prim[j]=0;
}
int main()
{
freopen("ciur.in","rt",stdin);
freopen("ciur.out","wt",stdout);
scanf("%d",&n);
primes(n);
for(i=2;i<=n;i++) if(prim[i]) nr++;
printf("%d",nr);
return 0;
}