# BZOJ 1597. [Usaco2008 Mar]土地购买

### Analysis:

```const int N = int(5e4) + 9;

VII II, I; LL f[N]; int q[N], cz, op;
int n;

#define k I[i].fi
#define x(j) I[j+1].se
#define y(j) f[j]
#define eval(j) ((LL)k*x(j)+y(j))

LL det(LL x1, LL y1, LL x2, LL y2){
return x1*y2 - x2*y1;
}

int dett(int p0, int p1, int p2){
LL t = det(x(p1)-x(p0), y(p1)-y(p0), x(p2)-x(p0), y(p2)-y(p0));
return t < 0 ? -1 : t > 0;
}

int main(){

#ifndef ONLINE_JUDGE
freopen("in.txt", "r", stdin);
//freopen("out.txt", "w", stdout);
#endif

II.resize(RD(n)); REP(i, n) RD(II[i].fi, II[i].se);

SRT(II); II.PB(MP(INF, 0)); I.PB(MP(0, INF)); REP(i, n){
while (I.back().se <= II[i].se) I.pop_back();
I.PB(II[i]);
}

/*n = SZ(I)-1; REP_1(i, n){
f[i] = INFF;
REP(j, i) checkMin(f[i], (LL)I[i].fi*I[j+1].se + f[j]);
cout << f[i] << endl;
}*/

n = SZ(I)-1; cz = 0, op = 0; REP_1(i, n){
while (cz < op && eval(q[cz]) >= eval(q[cz+1])) ++cz; f[i] = eval(q[cz]);
while (cz < op && dett(q[op-1], q[op], i) > 0) --op; q[++op] = i;
//cout << f[i] << endl;
}

cout << f[n] << endl;
}

```