C++ :

#include<bits/stdc++.h>
using namespace std;
long long cs[1000005],a,b,n,m,sj,ans,s;
int main(){
    cin>>n>>m;
    for(int i=1;i<=m;++i)
    {
    	scanf("%lld %lld",&a,&b);
    	cs[a]++;
    	cs[b+1]--;
    }
    for(int i=1;i<=n;++i)
    {
    	s+=cs[i];sj=s;
    	//cout<<s<<" ";
    	if(sj==0) ans++;
		while(sj>0)
		{
			sj=sj/10;
			ans++;
		}
    }
    cout<<ans;
    return 0;
}