How they think about this dp

codeforces round 600 div2 E problem
https://codeforces.com/contest/1253/problem/E
For the E problem:

int n,m;
cin>>n>>m;
for (int i=0;i<n;i++)
{
    int x,s;
    cin>>x>>s;
    le[i]=max(x-s,0);
    ri[i]=min(x+s,m);
}
for (int i=0;i<=m;i++)
{
    dp[i]=i;
    for (int j=0;j<n;j++)
    {
       if (le[j]<=i&&i<=ri[j]) 
       dp[i]=min(dp[i-1],dp[i]);
       else if (i>ri[j])
       dp[i]=min(dp[i],i-ri[j]+dp[max(0,le[j]-i+ri[j]-1)]);
    }
    cout<<i<<" "<<dp[i]<<endl;
}
cout<<dp[m];

}

In the above code, i dont clearly understand how the person come with this line of code, how they think about this-> dp[i]=min(dp[i],i-ri[j]+dp[max(0,le[j]-i+ri[j]-1)]); can somebody help me to understand this dp

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