hdu1009

#include <stdio.h> #include <algorithm> using namespace std;

struct Node { double j,f,p; } node[10000];

int cmp(Node x,Node y) { return x.p>y.p; }

int main() { int m,n; while(~scanf("%d%d",&n,&m) && (m!=-1 || n!=-1)) { double sum = 0,max = 0; int i,j; for(i = 0; i<m; i++) { scanf("%lf%lf",&node[i].j,&node[i].f); node[i].p = node[i].j/node[i].f; } sort(node,node+m,cmp); for(i = 0; i<m; i++) { if(n>node[i].f) { sum+=node[i].j; n-=node[i].f; } else { sum+=node[i].p*n; break; } } printf("%.3lf\n",sum); }

return 0; }