#include <iostream>
#include <vector>

std::vector<size_t> beolvas(std::istream &in) {
    size_t n;
    in >> n;

    std::vector<size_t> v(n);
    for (auto i = 0u; i < n; i++) {
        in >> v[i];
    }

    return v;
}

void feldolgoz(const std::vector<size_t> &v) {
    const auto n = v.size();

    size_t a = v[0];
    size_t b = a + v[1];
    for (auto i = 2; i < n; i++) {
        const auto c = v[i] + std::min(a, b);
        a = b;
        b = c;
    }

    std::cout << b << std::endl;
}

int main() {
    const auto v = beolvas(std::cin);
    feldolgoz(v);

    return 0;
}