#include <stdio.h>

int A[5000001],q[5000001],p,u;

int main()
{
FILE *in = fopen("deque.in","r");
FILE *out = fopen("deque.out","w");

int i,n,m;
long long s=0;

fscanf(in,"%d%d",&n,&m);
for (i=1;i<=n;i++) fscanf(in,"%d",&A[i]);

p=1;
u=0;

for (i=1;i<=n;i++)
{
while (p<=u && A[i]<=A[q[u]]) u--;
q[++u] = i;
if (i-m==q[p]) p++;
if (i>=m) s+=A[q[p]];
}
fprintf(out,"%lld",s);
}