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Cod sursa(job #345637)
#include<fstream.h>
#include<iostream.h>
int main()
{
unsigned long n,i,j,k=0;
char a[20000];
ifstream f("ciur.in",ios::in);
ofstream g("ciur.out",ios::out);
f>>n;
for(i=2; i<=n; i++)
a[i]=1;
for(i=2; i*i<=n; i++)
if(a[i]==1)
for(j=2; i*j<=n; j++)
a[i*j]=0;
for(i=2; i<=n; i++)
if(a[i]==1)k++;
g<<k;
f.close();
g.close();
return 0;
}