#include <stdio.h>
int per(int n,int r)
{
        int p=0,k;
        int d1=0;
        k=n-r;
        p=n*gop(n-1);
        d1=k*gop(k-1);
        return(p/d1);
}
int gop(int c)
{
        if(c!=1)
        return(c*gop(c-1));
        else
        return(1);
}
void main()
{
        int a,b;
        printf("input left");
        scanf("%d",&a);
        printf("input right(right #<left #)");
        scanf("%d",&b);
        printf("
}