#include<stdio.h>
#include<stdlib.h>
int n, k, d;
int p[100010], Gap[100010], lb, rb, sum, sum2, score;
void mergesort(int* po, int n){
int *pt, *pt2, *tmp;
int rm, rm2, h=0, i;
if(n<2) return;
pt=po;
pt2=po+n/2;
rm=n/2;
rm2=n-n/2;
mergesort(pt, rm);
mergesort(pt2, rm2);
tmp=(int*) malloc(sizeof(int)*n);
while(rm && rm2){
if(*pt>*pt2){
tmp[h++]=*(pt++);
rm--;
}
else{
tmp[h++]=*(pt2++);
rm2--;
}
}
while(rm){
tmp[h++]=*(pt++);
rm--;
}
while(rm2){
tmp[h++]=*(pt2++);
rm2--;
}
for(i=0; i<n; i++){
po[i]=tmp[i];
}
free(tmp);
return;
}
int main(){
int i, tmp;
scanf("%d %d %d", &n, &k, &d);
for(i=0;i<k;i++){
scanf("%d", &p[i]);
if(i) Gap[i-1]=p[i]-p[i-1]-1;
}
lb=p[0]-1;
rb=n-p[k-1];
mergesort(Gap, k-1);
for(i=0; i<k-1 && i<d/2-1; i++){
sum+=Gap[i];
}
sum2=sum+(k-1<=d/2-1 ? 0 : Gap[d/2-1]);
tmp=sum2;
if(score<tmp) score=tmp;
tmp=(lb>rb?lb:rb)+(d%2?sum2:sum);
if(score<tmp) score=tmp;
tmp=lb+rb+sum;
if(score<tmp) score=tmp;
printf("%d\n", score);
return 0;
}
