D - Redistribution

#include <iostream>
using namespace std;

#define MOD 1000000007
int dp[2000];

int main()
{
    int i,j,s;
    cin>>s;
    dp[0]=1;
    for(i=3;i<=s;i++){
        for(j=3;j<=i;j++){
            dp[i]+=dp[i-j];
            if(dp[i]>=MOD)
                dp[i]-=MOD;
        }
    }
    cout<<dp[s];
    return 0;
}