训练士兵 参考代码

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

typedef long long LL;
const int maxn = 1000000 + 100;
int n;
LL s, p, c, ans;
LL sum[maxn];

int main() {
#ifdef ExRoc
    freopen("test.txt", "r", stdin);
#endif // ExRoc
    ios::sync_with_stdio(false);

    cin >> n >> s;
    for (int i = 1; i <= n; ++i) {
        cin >> p >> c;
        sum[1] += p;
        sum[c + 1] -= p;
    }
    for (int i = 1; i < maxn; ++i) {
        sum[i] += sum[i - 1];
        ans += min(sum[i], s);
    }
    cout << ans << endl;

    return 0;
}