#include <stdio.h>

int main(){
	int result = 0;
	int value = 0;
	int vxod[999];
	//i`nt a = 0;
	for(int i = 0; i < 4; i++){
		scanf("%d",&value);;
		vxod[i] = value;
		//a = i;
	}
	//result = vxod[0];
	for(int i = 1; i < 4; i++){
		result = vxod[0] * result + vxod[i];
	}
	printf("%d\n", result);
	return 0;
}