[NOIP普及2013] 小朋友的数字

#include <cstdio>
#include <algorithm>
#include <cstring>
typedef long long ll;
int n;
ll a[1000005];
ll mod,dp[1000005],Max;
ll Sum[1000005];

const int INF = 0x3f3f3f3f;

int main(){
    scanf("%d%lld",&n,&mod);
    for(int i=1;i<=n;++i){
        scanf("%lld",&a[i]);
        dp[i] = std::max(dp[i-1]+a[i],a[i]);
    } 
    for(int i=2;i<=n;++i){
        dp[i] = std::max(dp[i-1],dp[i]);
        //printf("dp[%d]:%lld\n",i,dp[i]);
        //printf("i:%d - %lld\n",i,Max);
    }
    Sum[1] = dp[1];
    Sum[2] = dp[1] + dp[1];
    bool flag=0;
    //for(int i=1;i<=n;++i) printf("dp[%d]:%lld\n",i,dp[i]);
    for(int i=3;i<=n;i++){
        Sum[i]+=Sum[i-1];
        if(dp[i-1] > 0) Sum[i]+=dp[i-1];
        if(Sum[i] > Sum[1]) flag=1;
        if(flag==1) Sum[i]%=mod;
    }
    //for(int i=1;i<=n;i++) printf("dp[%d]:%lld\n",i,Sum[i]);
    if(flag) printf("%lld\n",Sum[n]);
    else printf("%lld\n",Sum[1]);
    return 0;
}