# include <stdio.h>

long int n;

void citire()
{
FILE *f=fopen("dame.in","r");
fscanf(f,"%ld",&n);
fclose(f);
}

void scrie_1()
{
FILE *g=fopen("dame.out","w");
fprintf(g,"1\n1 1\n");
}

void scrie_3()
{
FILE *g=fopen("dame.out","w");
fprintf(g,"2\n1 1\n3 2\n");
}

void scrie()
{
long int i=2,j;
FILE *g=fopen("dame.out","w");
fprintf(g,"%ld\n",n);
for (j=1;j<=n;j++)
	{
	fprintf(g,"%ld %ld\n",i,j);
	i+=2;
	if (i>n) i=1;
	}
}

int main()
{
citire();
if (n<=1) scrie_1();
else if (n==3) scrie_3();
else scrie();
fcloseall();
return 0;
}