#include <bits/stdc++.h>
using namespace std;

#define dbg(x) write(#x " = "), write(x), write("\n")
#define getch() (maxip == ip ? EOF : (*ip++))
#define putch(x) (*op++) = (x)
#define writeln(...) write(__VA_ARGS__), putch('\n')

char inp[1 << 24], *ip = inp, *maxip;
char outp[1 << 20], *op = outp;
int readtime, precision = 6;

inline void main_init();
inline char getchigws();
template <typename T, typename... Args> void read(T& x, Args&... args);
void read();
template <typename T> void read(T& x);
template <> void read<double>(double& x);
template <typename T, typename... Args>
void write(const T& x, const Args&... args);
void write();
template <typename T> void write(const T& x);
template <> void write<double>(const double& x);
template <> void write<char>(const char& ch);
void write(const char* s);
// define fast io

int main()
{
    main_init();
    int n, m;
    read(n, m);
    int L, R, Min = INT_MAX, Max = INT_MIN;
    for (int i = 1; i <= m; i++)
        read(L, R), Min = min(Min, R), Max = max(Max, L);
    writeln(max(Min - Max + 1, 0));
#ifdef LOCAL
    main_init();
    fprintf(stderr, "Time used = %.2f\n",
            ( double )(clock() - readtime) / CLOCKS_PER_SEC);
    while (1)
        ;
#else
    main_init();
#endif
    return 0;
}

inline void main_init()
{
    static bool inited = false;
    if (inited)
        fwrite(outp, 1, op - outp, stdout), op = outp;
    else
    {
        maxip = ip + fread(inp, 1, sizeof(inp), stdin) + 1;
        readtime = clock();
        inited = true;
    }
}

inline char getchigws()
{
    char ch;
    while (isspace(ch = getch()))
        ;
    return ch;
}

template <typename T, typename... Args> void read(T& x, Args&... args)
{
    read(x);
    read(args...);
}

void read() {}

template <typename T> void read(T& x)
{
    T f = 1;
    int ch;
    while (!isdigit(ch = getch()) && ch != EOF)
        if (ch == '-')
            f = -1;
    x = 0;
    while (isdigit(ch) && ch != EOF)
        x = (x << 1) + (x << 3) + (ch ^ 48), ch = getch();
    ip--;
    x *= f;
}

template <> void read<double>(double& x)
{
    double l = 0, r = 0, f = 1;
    int s = 0, ch;
    while (!isdigit(ch = getch()) && ch != EOF)
        if (ch == '-')
            f = -1;
    while (isdigit(ch) && ch != EOF)
    {
        l = l * 10 + (ch ^ 48);
        ch = getch();
    }
    if (ch == '.')
        while (isdigit(ch = getch()) && ch != EOF)
            r = r * 10 + (ch ^ 48), s++;
    ip--;
    x = (l + r / pow(10, s)) * f;
}

template <typename T, typename... Args>
void write(const T& x, const Args&... args)
{
    write(x);
    write(args...);
}

void write() {}
template <typename T> void write(const T& x)
{
    if (x < 0)
        putch('-'), write(-x);
    else
    {
        if (x >= 10)
            write(x / 10);
        putch(x % 10 ^ 48);
    }
}

template <> void write<double>(const double& x)
{
    if (x == 0)
    {
        write("0.");
        for (int i = 0; i < precision; i++)
            putch('0');
        return;
    }
    if (x < 0)
        putch('-'), write(-x);
    else
    {
        double r = x - floor(x), l = floor(x);
        if (l == 0)
            putch('0');
        char buf[310];
        int i = 0;
        while (floor(l) != 0)
        {
            buf[i++] = floor(l - floor(l / 10) * 10);
            l /= 10;
        }
        for (int j = i - 1; j >= 0; j--)
            putch(buf[j] ^ 48);
        putch('.');
        for (int i = 0; i < precision - 1; i++)
            putch(int(floor(r *= 10)) ^ 48), r -= floor(r);
        double tmp = r * 10;
        if (int(floor(tmp * 10 - floor(tmp) * 10)) >= 5)
            putch((int(floor(tmp)) + 1) ^ 48);
        else
            putch(int(floor(tmp)) ^ 48);
    }
}

template <> void write<char>(const char& ch) { putch(ch); }

void write(const char* s)
{
    while (*s)
        putch(*s++);
}

Measured memory_bytes: 3328