#include <bits/stdc++.h>
using namespace std;
const int MAX=1000000007;
int main() {
    long long n,k;
    //freopen("QUASONG.INP","r",stdin);
    //freopen("QUASONG.OUT","w",stdout);
    cin>>n>>k;
    long long a[200001]={0}; 
    a[1]=1;
    for (long long i=1;i<n;i++) {
        for (long long j=0;j<k;j++) {
            long long l,r;
            cin>>l>>r;
            for (long long k=l;k<=r;k++) 
                if (i+k<=n) 
                    a[i+k]=(a[i+k]+a[i])%MAX;
        }
    }
    cout<<a[n];
    return 0;
}