#include<stdio.h>
int main(void)
{
    int n;
    int res=0;
    int school[3000],extracurricular[3000];
    int sum[3000];
    int happy[3000];
    scanf("%d",&n);
    for(int i=0;i<n;i++)
    {
        scanf("%d %d",&school[i],&extracurricular[i]);
        sum[i]=school[i]+extracurricular[i];
    }
    happy[0]=sum[0]-8;
    res+=happy[0];
    for(int i=1;i<n;i++)
    {
        happy[i]=happy[i-1]+sum[i]-8;
        res+=happy[i];
    }
    printf("%d",res);
    return 0;
}