#include <stdio.h>
using namespace std;
void decizie(int n){
freopen("dame.out","r",stdout);
if (n == 3)
printf("2\n1 1\n2 3");
else if (n == 2 || n == 1)
printf("1\n1 1");
else if(n%6==2){
printf("%d\n",n);
int i,j;
for(i=1,j=2;j<=n && i<=n; ++i ,j+=2)
printf("%d %d\n",i,j);
printf("%d 3\n",i);
++i;
printf("%d 1\n",i);
++i;
for(j=7;j<=n && i<=n;++i,j+=2)
printf("%d %d\n",i,j);
printf("%d 5\n",i);
}
else if(n%6==3){
int i, j;
printf("%d\n",n);
for (i=1,j=4;j<=n && i<=n;++i,j+=2)
printf("%d %d\n",i,j);
printf("%d 2\n",i);
++i;
for (j=5;j<=n && i<=n;++i,j+=2)
printf("%d %d\n",i,j);
printf("%d 1\n",i);
++i;
printf("%d 3\n",i);
}
else{
int i, j;
printf("%d\n",n);
for (i=1,j=2;j<=n && i<=n;++i,j+=2)
printf("%d %d\n",i,j);
for (j=1;j<=n && i<=n;++i,j+=2)
printf("%d %d\n",i,j);
//printf("%d %d\n",i,j);
}
fclose(stdout);
}
int main(){
int n;
freopen("dame.in","r",stdin);
scanf("%d",&n);
fclose(stdin);
decizie(n);
return 0;
}