#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<cstring> // strcpy()\strcat()\strcmp()\strlen()\memset() #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ int s=0,n; cin>>n; int a[n],b[n]; for(int i=1;i<=n-1;i++){ cin>>a[i]>>b[i]; s+=a[i]*b[i]; } cout<<s; return 0; }