#include <bits/stdc++.h> using namespace std; long long n; double a[100002],b[100002]; double sum,t,m,total; bool d=false; int main() { scanf("%lld",&n); for(int i=1; i<=n; i++) { scanf("%lf%lf",&a[i],&b[i]); if(a[i]*0.1*b[i]>a[i]||a[i]<=0||b[i]<=0) d=true; sum+=a[i]*0.1*b[i]; total+=a[i]; } scanf("%lf%lf",&t,&m); if(m>t) { printf("error\n"); return 0; } if(d==true) { printf("error\n"); return 0; } if(total>=t) total-=m ; printf("%.2lf\n",min(total,sum)); return 0; }