chore: solved hard day 13 task

medium/day_13/solution.cpp

@@ -1 +1,32 @@
-//write your code here
+//write your code here
+
+
+#include <iostream>
+using namespace std;
+long long int a[1000002]={0};
+int main() {
+    // cout<<5;
+    long long int n;
+    cin>>n;
+    long long int mod=1000000007;
+
+    long long int i,s;
+    s=0;
+    a[0]=0;
+    a[1]=1;
+    a[2]=2;
+    s=3;
+    for(i=3;i<=n;i++)
+    {
+        a[i]=(a[i]+a[i-1]+1)%mod;
+        s=(s+a[i])%mod;
+        a[i]=(a[i]+a[i-2])%mod;
+    }
+    if(n==1)
+    cout<<1;
+    else if(n==2)
+    cout<<3;
+    else
+    cout<<s;
+        return 0;
+}