#include <stdio.h>  
const int n_max = 1000;  
long long c[n_max][n_max],  
          p[n_max][n_max];  
int i, j, n, d;  
long long a, b;  
int main()  
{  
    freopen("bile.in","r", stdin);  
    freopen("bile.out", "w", stdout);  
    scanf("%d %d", &n, &d);  
    scanf("%lld %lld", &a, &b);  
    c[0][0] = 1;      
    for (i = 1; i <= n; ++ i)  
    {  
        p[1][i] = 1;  
        c[i][0] = 1;  
        for (j = 1; j <= i; ++ j)  
            c[i][j] = c[i-1][j-1] + c[i-1][j];  
    }  
    for (i = 2; i <= n; ++ i)  
        for (j = i; j <=n; ++ j)  
            p[i][j] = p[i][j-1] + p[i-1][j-d-1];  
    for (i = 2; i <= n; ++ i)  
    {  
        int sum = 0;  
        for (j = 1; j <= n; ++ j)  
            sum += p[i][j];  
/*      printf("i = %d sum = %d\n",i, sum); 
        fflush(stdout); 
*/      if (((c[n][i]-sum)/c[n][i]) > (a/b))  
        {  
            printf("%d\n",i);  
            return 0;  
        }  
    }  
    printf("%d\n", (n/(d+1))+1);  
    return 0;  
}