#include <iostream>
using namespace std;
int main() {
int n, sumEvenNo = 0, sumOddNo = 0;
cin >> n;
for (int i = 1; i <= n; ++i) {
int num;
cin >> num;
if (i % 2 == 0) {
sumEvenNo += num;
} else {
sumOddNo += num;
}
}
cout << sumEvenNo - sumOddNo;
return 0;
}
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