#include<bits/stdc++.h> using namespace std; int main(){ int n; cin>>n; int a[n],b[n],c[n]; int mincost=20000,totalcost=0; for(int i=0;i<n;i++){ cin>>a[i]>>b[i]; c[i]=a[i]+(i>0?b[i-1]:0); mincost=min(mincost,c[i]); totalcost+=mincost; } cout<<totalcost; return 0; }