import std.stdio, std.array, std.string, std.conv, std.algorithm;
import std.typecons, std.range, std.random, std.math, std.container;
import std.numeric, std.bigint, core.bitop, core.stdc.string;

void main() {
    auto N = readln.chomp.to!int;
    auto A = iota(N-1).map!(_ => readln.split.map!(to!int).array).array;

    auto x = A.map!(a => a[0]).sum;
    auto y = A.map!(a => a[1]).sum;

    int ub = y;
    int lb = max(0, y - x);

    writeln(ub - lb + 1);
}