usaco Number Triangles

/*
ID: modengd1
PROG: numtri
LANG: C++
*/
#include <iostream>
#include <stdio.h>
#include <memory.h>
using namespace std;
int dp[2][1000],input[1001];

int main()
{
    freopen("numtri.in","r",stdin);
    freopen("numtri.out","w",stdout);
    int N;
    scanf("%d",&N);
    memset(dp,0,sizeof(dp));
    for(int i=0;i<N;i++)
    {
        for(int j=0;j<=i;j++)
        {
            scanf("%d",&input[j]);
            if(j==0)
                dp[(i+1)%2][j]=dp[i%2][j]+input[j];
            else
                dp[(i+1)%2][j]=max(dp[i%2][j]+input[j],dp[i%2][j-1]+input[j]);
        }
    }
    int ans=0;
    for(int i=0;i<N;i++)
        ans=max(max(ans,dp[0][i]),dp[1][i]);
    cout<<ans<<endl;
    return 0;
}