80分,求助

#include<bits/stdc++.h>
#define ll long long
using namespace std;
ll a[100005],n,m;
bool check(ll x)
{
    ll kkk=1;
    ll summ=a[1];
    for(ll i=2;i<=n;i++)
    {
        summ+=a[i];
        if(summ>x)
        {
            summ=a[i];
            kkk++;
        }
        if(kkk>m)
            return false;
    }
    /*	if(kkk<m)
        return false;*/
    return true;
}
int main()
{
    //freopen("11.in","r",stdin);
    //freopen("11.out","w",stdout);
    ll ans;
    scanf("%lld%lld",&n,&m);
    for(ll i=1;i<=n;i++)
    {
        scanf("%lld",&a[i]);
    }
    ll l=1,r=0;
    for(ll i=1;i<=n;i++)
        r+=a[i];
    while(l<=r)
    {
        ll mid=(l+r)>>1;
        if(check(mid))
        {
            ans=mid;
            r=mid-1;	
        }	
        else
            l=mid+1;		
    }
    printf("%lld\n",ans);
    return 0;
}