暴力解决

#include <iostream>
#include <algorithm>
using namespace std;
const int N = 300005;
typedef long long ll;
ll f[N],t[N],c[N];
int q[N];
int main(){
    int n,s;
    scanf("%d%d",&n,&s);
    for(int i = 1;i <= n;i++){
        scanf("%lld%lld",&t[i],&c[i]);
        t[i] += t[i-1],c[i] += c[i-1];
    }
    int hh = 0,tt = 0;
    for(int i = 1;i <= n;i++){
        int l = hh,r = tt;
        while(l < r){
            int mid = l + r >> 1;
            if(f[q[mid+1]]-f[q[mid]]<=(t[i]+s)*(c[q[mid+1]]-c[q[mid]]))     l = mid + 1;
            else    r = mid;
        }
        f[i] = f[q[l]] - (t[i] + s) * c[q[l]] + c[i] * t[i] + s * c[n];
        while(hh < tt && (f[q[tt]]-f[q[tt - 1]])*(c[i]-c[q[tt]]) >= (f[i]-f[q[tt]])*(c[q[tt]]-c[q[tt - 1]]))    tt--;
        q[++tt] = i;
    }
    printf("%lld\n",f[n]);
    return 0;
}