#include<stdio.h>
#include<string.h>
int main () {
	char c[1000000];
	int n,i,j,nr=0,s=0;
	FILE *in=fopen("fractii.in","r"), *out=fopen("fractii.out","w");
	fscanf(in,"%d",&n);
	memset(c,1,(n+1)*sizeof(c[0]));
	c[0]=0;
	c[1]=0;
	for(i=2;i<=n;i++)
		if(c[i])
			for(j=i+i;j<=n;j+=i)
				c[j]=0;
	for(i=2;i<=n;i++){
		for(j=2;j<=i;j++)
			if(c[j])
				nr++;
		s+=nr;
		nr=0;
	}
	s=s*2+1;
	fprintf(out,"%d",s);
	fclose(in);
	fclose(out);
	return 0;
}