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Cod sursa(job #234585)
#include <stdio.h>
#include <math.h>
FILE *f,*g;
long p[2000000];
int main()
{
f=fopen("ciur.in","r");
g=fopen("ciur.out","w");
long n,i,j,k=0;
fscanf(f,"%ld",&n);
i=2;
while(i<=sqrt(n)){ if(p[i]==0){ for(j=i+i;j<=n;j=j+i) p[j]=1;
i++;
}
else i++;
}
for(i=1;i<=n;i++) if(p[i]==1) k++;
fprintf(g,"%ld",k);
fclose(f);
fclose(g);
return 0;
}