#include <bits/stdc++.h>
using namespace std;

int main(void){
    int N;
    cin >> N;
    vector<long long> C(N);
    vector<long long> D(N);
    long long sum = 0;
    for (int i = 0; i < N; i++) {
        cin >> C[i] >> D[i];
        sum += C[i] + D[i];
    }
    
    const long long INF = 1e16;
    vector<vector<long long>> dp(N+1, vector<long long>(2, INF));
    dp[0][1] = sum-D[0];
    for (int i = 1; i <= N; i++) {
        dp[i][0] = min(dp[i-1][1] + C[i-1], dp[i-1][0]);
        dp[i][1] = min(dp[i-1][1], dp[i][0] - D[i]);
    }
    cout << dp[N][0] << endl;
}