#include <cstdio>

#define MAXN 1000

int main(){
    int n;
    FILE *fin, *fout;
    fin=fopen("dame.in", "r");
    fout=fopen("dame.out", "w");
    fscanf(fin, "%d", &n);

    if(n<3) fprintf(fout, "1\n1 1\n");
    else if(n==3) fprintf(fout, "2\n1 1\n2 3\n");
    else{
        fprintf(fout, "%d\n", n);
        for(int i=1; i<=n; i++){
            int j;
            if(i<=n/2) j=2*i;
            else j=2*(i-n/2)-1;
            fprintf(fout, "%d %d\n", i, j);
        }
    }

    fclose(fin);
    fclose(fout);
    return 0;
}