num_sets=int(input()) #Number of sets of data
timel=list() #Creates empty list
speedl=list() #Creates empty list
distancel=list() #Creates empty list

for i in range (num_sets):  #For each set of data, inputs speed and time into appropriate lists
    speed,time=input().split() #Makes two inputs one line
    timel.append(time) #Adds time to time list
    speedl.append(speed) #Adds speed to speed list
for i in range (len(timel)): #Multiplies i'th values of each list
    distancel.append(int(timel[i])*int(speedl[i])) #Adds multiplied value to distance list

total= sum(distancel) #Total distance