#include<iostream>
using namespace std;
int main()
{
	int n,s,t,t0,i,sum;
	while(cin>>n)
	{
		if(n==-1)
			break;
		sum=0;
		t0=0;
		for(i=0;i<n;i++)
		{
			cin>>s>>t;
			sum+=s*(t-t0);
			t0=t;
		}
		cout<<sum<<" miles\n";
	}
	return 0;
}

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