#include <bits/stdc++.h>
using ll = long long;
int main()
{
    int N;
    std::cin >> N;
    std::vector<ll> C(N), D(N);
    for (int i = 0; i < N; i++) { std::cin >> C[i] >> D[i]; }
    std::vector<ll> dp{0, C[0]};
    for (int i = 1; i < N; i++) { dp[0] = std::min(dp[0] + D[i], dp[1]), dp[1] = std::min(dp[0] + C[i], dp[1] + D[i]); }
    std::cout << dp[1] + std::accumulate(C.begin(), C.end(), 0LL) << std::endl;
    return 0;
}