atcoder-nov beg- A no

#include<stdio.h>

long long int sum(long long int n)
{
    return n*(n+1)/2;
}

int main()
{
    long long int n;
    scanf("%lld", &n);

    long long int i, a[n], b[n];
    for(i = 0; i < n; i++) scanf("%lld %lld", &a[i], &b[i]);

    long long int s = 0;
    for(i = 0; i < n; i++)
    {
        s += sum(b[i]) - sum(a[i] - 1);
    }
    printf("%lld\n", s);
}