Coffee shops

#include <iostream>
#include <algorithm>
using namespace std;
int main() {
    int n;
    cin >> n;

    int pp1, pp0, p1, p0, c1, c0, a;

    cin >> pp1;
    pp0 = 0;

    if (n == 1) {
        cout << pp1 << "\n";
        return 0;
    }

    cin >> p1;
    p0 = pp1;

    if (n == 2) {
        cout << std::min(p1, p0) << "\n";
        return 0;
    }

    c0 = -1; c1 = -1;

    //cout << pp1 << " " << pp0 << " " << p1 << " " << p0 << "\n";

    for (int i=2; i<n; ++i) {
        cin >> a;
        if (i < 3) {
            c1 = std::min(p1, p0) + a;
        }
        else {
            c1 = std::min(pp0, std::min(p1, p0)) + a;
        }
        c0 = p1;

        //cout << c1 << " " << c0 << "\n";

        pp1 = p1; pp0 = p0;
        p1 = c1; p0 = c0;
    }
    cout << std::min(c1, c0) << "\n";
}

Test 1

Verdict: UNKNOWN

Test 2

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Test 3

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Test 4

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Test 5

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Test 6

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Test 7

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Test 8

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Test 9

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Test 10

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Test 11

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Test 12

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Test 13

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Test 14

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Test 15

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Test 16

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Test 17

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Test 18

Verdict: UNKNOWN