#include "cstdio"

using namespace std;

int st[100010];

void sortare(int n,int st[])
{
    int aux;
    for(int i=0;i<n-1;i++)
        for(int j=i+1;j<n;j++)
            if(st[i]>st[j])
            {
                aux=st[i];
                st[i]=st[j];
                st[j]=aux;
            }
}

int solutii(int n,int st[])
{
    int nr=0;
    for(int i=0;i<n-2;i++)
    {
        for(int j=i+1;j<i+3;j++)
            break;
        nr++;
    }

    return nr;
}

int main()
{
    int N,i;
    FILE* fin=fopen("nrtri.in","r");
    FILE* fout=fopen("nrtri.out","w");

    fscanf(fin,"%d",&N);
    if(N>=1 && N<=150)
    {
        for(i=0;i<N;i++)
            fscanf(fin,"%d",&st[i]);

        sortare(N,st);

        fprintf(fout,"%d",solutii(N,st));

        fclose(fin);
        fclose(fout);

        return 0;
    }

    else
        return 0;
}