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

// dfmt off
T lread(T = long)(){return readln.chomp.to!T();}
T[] aryread(T = long)(){return readln.split.to!(T[])();}
void scan(TList...)(ref TList Args){auto line = readln.split();
foreach (i, T; TList){T val = line[i].to!(T);Args[i] = val;}}
alias sread = () => readln.chomp();enum MOD = 10 ^^ 9 + 7;
// dfmt on

void main()
{
    long n, m;
    scan(n, m);
    auto b = new bool[](n);
    long L = 1;
    long R = n;
    foreach (_; 0 .. m)
    {
        long l, r;
        scan(l, r);
        L = max(l, L);
        R = min(r, R);
    }
    max(R - L + 1, 0).writeln();
}
