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Cod sursa(job #996868)
#include <stdio.h>
#include <stdlib.h>
char v[200000000];
int main()
{ FILE*fi,*fout;
int con,n,i,j;
fi=fopen("ciur.in" ,"r");
fout=fopen("ciur.out" ,"w");
fscanf(fi,"%d" ,&n);
for(i=2;i*i<=n;i++)
if(v[i]==0)
for(j=i*i;j<=n;j=j+i)
v[j]=1;
con=0;
for(i=2;i<=n;i++)
if(v[i]==0)
con++;
fprintf(fout,"%d" ,con);
fclose(fi);
fclose(fout);
return 0;
}