#pragma GCC optimize("Ofast")
#pragma GCC target("avx2")

#define getrp() ({char*mmap();mmap(0l,1l<<25,1,2,0,0ll);})
#define rd() ({long _v=0,_c;while(_c=*rp++-48,_c>=0)_v=_v*10+_c;_v;})
#define wt(v) ({ulong _z=v;do*--wp=_z%10+48;while(_z/=10);})
#define wt1(v) ({char wbuf[64],*wp=wbuf+sizeof wbuf;wt(v);write(1,wp,wbuf+sizeof wbuf-wp);})
#define rep(v,e) for(long v=0;v<e;++v)

typedef unsigned long ulong;

long a[100000];

int main(){
	char*rp=getrp();
	long n=rd();
	long k=rd();
	rep(i,n){
		a[i]=rd();
	}
	long l=0,r=100001000000001l;
	while(l+1<r){
		long m=l+r>>1;
		long o=0;
		long t=0;
		rep(i,n){
			long j=i+1;
			long d=m-(a[i]+o);
			if(d>0){
				long e=(d-1)/j+1;
				o+=e*j;
				t+=e;
				if(t>k){
					goto dame;
				}
			}
		}
		if(1){
			l=m;
		}else{
			dame:;
			r=m;
		}
	}
	wt1(l);
	_exit(0);
}