#include <stdio.h>
int main(){ 
	long long sum=0,x,y,z;
	scanf("%lld%lld%lld",&x,&y,&z);
	if(z==10){
	printf("%d",(x-1)*10>=(y-1)?(y-1):(x-1)*10);return 0;}
    while(z>10){
		z-=10;
		sum+=y-1;
	}
	if(z<10){
		sum+=(x-1)*z;
	}
	printf("%lld",sum);
	return 0;
}