This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
//#include<bits/extc++.h>
//__gnu_pbds
const int MOD = 1000000007;
const int N = 5e5+5;
ll dp[N][26];
deque<int> belongs[4];
ll re[4][26];
void remove(int v,int k){
for(int c=0;c<26;c++){
re[k][c]-=dp[v][c];
re[k][c]%=MOD;
}
}
void add(int v,int k){
//cout<<"adding "<<v<<" to "<<k<<":";
for(int c=0;c<26;c++){
re[k][c]+=dp[v][c];
re[k][c]%=MOD;
//cout<<re[k][c]<<" ";
}
//cout<<"\n";
}
vector<int> ran[N][2];
void printbelongs(){
cout<<"--------------------\n";
cout<<"printing...:\n";
for(int k=0;k<4;k++){
for(auto i : belongs[k]) cout<<i<<" ";
cout<<"\n";
}
cout<<"--------------------\n";
}
void mantain(int r,bool t){
if(t){
stack<int> f10;
stack<int> f11;
while(belongs[0].size() && belongs[0][0]<=r){
f10.push(belongs[0][0]);
remove(belongs[0][0],0);
belongs[0].pop_front();
}
while(belongs[1].size() && belongs[1][0]<=r){
f11.push(belongs[1][0]);
remove(belongs[1][0],1);
belongs[1].pop_front();
}
while(f10.size()){
belongs[2].push_front(f10.top());
add(belongs[2][0],2);
f10.pop();
}
while(f11.size()){
belongs[3].push_front(f11.top());
add(belongs[3][0],3);
f11.pop();
}
}else{
stack<int> f01;
stack<int> f11;
while(belongs[0].size() && belongs[0][0]<=r){
f01.push(belongs[0][0]);
remove(belongs[0][0],0);
belongs[0].pop_front();
}
while(belongs[2].size() && belongs[2][0]<=r){
f11.push(belongs[2][0]);
remove(belongs[2][0],2);
belongs[2].pop_front();
}
while(f01.size()){
belongs[1].push_front(f01.top());
add(belongs[1][0],1);
f01.pop();
}
while(f11.size()){
belongs[3].push_front(f11.top());
add(belongs[3][0],3);
f11.pop();
}
}
}
int main(){
ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);
int n,m;cin>>n>>m;
for(int i=0;i<m;i++){
int a,b;cin>>a>>b;
bool w= 0;
if(a>b){w=1;swap(a,b);}
ran[a+1][w].push_back(b);
}
for(int i=n;i>=1;i--){
belongs[0].push_front(i);
for(int c=0;c<26;c++){
if(i==n) dp[i][c]=1;
else{
for(int f=0;f<26;f++){
for(int k=0;k<4;k++){
if(k==0 && f!=c) dp[i][c]+=re[k][f];
if(k==1 && f>c) dp[i][c]+=re[k][f];
if(k==2 && f<c) dp[i][c]+=re[k][f];
dp[i][c]%=MOD;
}
}
dp[i][c]++;
dp[i][c]%=MOD;
}
//cout<<dp[i][c]<<" ";
}
//cout<<"\n";
add(i,0);
for(int b=0;b<2;b++){for(auto v : ran[i][b]) mantain(v,b);}
// printbelongs();
}
ll ans = 0;
for(int i=0;i<26;i++) ans=(ans+dp[1][i])%MOD;
cout<<ans<<"\n";
return 0;
}
// abba works...
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