C++ :

#include<cstdio>
#include<cstring>
#include<cstdlib>
typedef __int128 LL;
const int N=1100000;
int n, p;
LL a[N];
LL b[N],c[N];
const int SIZE=1<<25;
char Buf[SIZE],*buf=Buf;
#define getint(x) (x)=strtoll(buf,&buf,10)
int main()
{
    fread(Buf,SIZE,1,stdin);
    getint(n);getint(p);
    for (int i=1;i<=n;i++)
        getint(a[i]);
    b[1]=a[1];
    LL now=a[1]>0?a[1]:0;
    for(int i=2;i<=n;i++)
    {
        b[i]=b[i-1];
        now+=a[i];
        b[i]=now>b[i]?now:b[i];
        now=now>0?now:0;
    }
    c[1]=b[1];
    c[2]=c[1]+b[1];
    for(int i=3;i<=n;i++)
        c[i]=c[i-1]+(b[i-1]>0?b[i-1]:0);
    printf("%d\n", (int)((c[n]>c[1]?c[n]:c[1])%p));
    return 0;
}