第一个测试数据不对，找大神求原因

#include<stdio.h>
#include <iostream>
using namespace std;
int main()
{
    int l, m;
    int u[200], v[200];
    cin >> l >> m;
    for (int i = 1; i <= m; i++)
    {
        cin >> u[i] >> v[i];
    }
    int length[100001];
    for (int i = 1; i <= l; i++)
        length[i] = 1;
    for (int i = 1; i <= m; i++)
    {
        while( u[i] <= v[i])
        {
            if (length[u[i]] != 0)
            {
                length[u[i]] = 0;
                l--;
            }
            u[i]++;
        }
    }
    cout << l+1;
    return 0;
}