N=int(input())
s=0
for i in range(N):
    x,y=map(int,input().split())
    s*=10
    s+=(x+y)
print(s)

s is one digit by definition

But if a+b>=10 s can be expressed only using two digits

Ohh, wait...

Try print(int(s))

I suppose you print in scientific notation when s is huge