Which Line?

#include <bits/stdc++.h>

using namespace std;

int vals[300000][2];
int memo[300000][2];
long long ans;

long long solve(int n, int k) {
    // compute and solve answer here
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < 2; j++) {
            ans = 0;
            if (i == 0) {
                ans = vals[i][j];
            }
            else {
                ans = vals[i][j] + min(memo[i - 1][j], k + memo[i - 1][1 - j]);
            }
            memo[i][j] = ans;
        }
    }
    return min(memo[n - 1][0], memo[n - 1][1]);
}

int main() {
    int n, k, i, j;
    cin >> n >> k;
    for(i = 0; i < n; i++) {
        for(j = 0; j < 2; j++) {
            // use scanf to avoid TLE
            scanf("%d",&vals[i][j]);
        }
    }

    cout << solve(n,k) << endl;
}