POJ2393(贪心)

水题，compare current storing value and the price of that day, if cheaper then assign, if not then update the store value.

//#define LOCAL

#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

int main(void){
#ifdef LOCAL
    freopen("data.in", "r", stdin);
#endif 
    int n, c, s, y;
    long long store = -1;
    long long ans = 0;

    scanf("%d%d", &n, &s);
    for(int i = 0; i < n; i++){
        scanf("%d%d", &c, &y);

        if(store == -1 || store > c)
            store = c;

        ans += store * y;
        store += s;
    }

    printf("%lld\n", ans);
    return 0;
}