#include <bits/stdc++.h>
using namespace std;
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
freopen("MAGICSUM.inp", "r", stdin);
freopen("MAGICSUM.ans", "w", stdout);
long long ans = 0;
int n; cin >> n;
for(int i = 1; i <= n; i++){
int l, r; cin >> l >> r;
for(int j = l; j <= r; j++) ans += j;
}
cout << ans;
return 0;
}
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